Anti-flt-1 antibodies for treating duchenne muscular dystrophy

ABSTRACT

The present invention provides, among other things, anti-Flt-I antibodies and methods for treating muscular dystrophy, in particular, Duchenne muscular dystrophy (DMD). In some embodiments, a method according to the present invention in-cludes administering to an individual who is suffering from or susceptible to DMD an effective amount of an anti-Flt-I antibody or antigen-binding protein thereof such that at least one symptom or feature of DMD is reduced in intensity, severity, or frequency, or has delayed onset.

RELATED APPLICATIONS

This application is a continuation of Ser. No. 15/564,976, filed Oct. 6, 2017, which is a 35 U.S.C. § 371 National Stage Application of International Application No. PCT/US16/26352, filed Apr. 7, 2016, which claims priority to U.S. Provisional Application Ser. No. 62/144,251, filed Apr. 7, 2015, and U.S. Provisional Application Ser. No. 62/307,645, filed Mar. 14, 2016, the disclosure of each of which is hereby incorporated by reference.

INCORPORATION-BY-REFERENCE OF SEQUENCE LISTING

The content of the text file named “SHR-1189US_ST25.txt”, which was created on Oct. 6, 2017 and is 168 KB in size, is hereby incorporated by reference in its entirety.

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder affecting an estimated 1:3600 male births with an estimated 50,000 affected individuals worldwide. The disorder is marked by a progressive wasting of the muscles and affected children are wheelchair dependent by the time they reach 13 years of age. Affected individuals usually present with symptoms at 3 years of age with the median survival for such individuals being between 25 and 30 years of age. Respiratory failure due to diaphragmatic weakness and cardiomyopathy are common causes of death.

DMD is caused by a mutation in the dystrophin gene. The dystrophin gene is located on the X chromosome and codes for the protein dystrophin. Dystrophin protein is responsible for connecting the contractile machinery (actin-myosin complex) of a muscle fiber to the surrounding extracellular matrix through the dystroglycan complex. Mutations in the dystrophin gene result in either alteration or absence of the dystrophin protein and abnormal sarcolemal membrane function. While both males and females can carry a mutation in the dystrophin gene, females are rarely affected with DMD.

One characteristic of DMD is ischemia of the affected tissues. Ischemia is a restriction or decrease in blood supply to tissues or organs, causing a shortage of oxygen and nutrients need for cellular metabolism. Ischemia is generally caused by constriction or obstruction of blood vessels resulting in damage to or dysfunction of the tissue or organ. Treatment of ischemia is directed toward increasing the blood flow to the affected tissue or organ.

Presently, there is no cure for DMD. Several therapeutic avenues have been investigated including gene therapy and corticosteroid administration, however the need for alternatives for DMD patients still exists.

SUMMARY OF INVENTION

The present invention provides, among other things, improved methods and compositions for treating muscular dystrophy, in particular, Duchenne muscular dystrophy (DMD) and/or Becker muscular dystrophy based on anti-Flt-1 antibody therapy. As described in the Examples below, the invention is, in part, based on the discovery that anti-Flt-1 antibodies, or antigen-binding fragments thereof, can inhibit VEGF and other ligands from binding to the Flt-1 receptor, thereby increasing the amount of VEGF and/or other ligands available to bind to VEGF receptors. Increased availability of VEGF promotes angiogenesis with increased blood flow to muscle to combat functional ischemia and leading to improvements in structural and functional characteristics of DMD. Indeed, as shown in the present Examples, the present inventors have demonstrated that administration of the anti-Flt-1 antibody improves measures of muscle pathology (e.g., improved angiogenesis, reduced fibrosis, reduced necrosis). Therefore, the present invention provides safe and effective antibody-based therapeutics for the treatment of DMD.

In one aspect, the invention provides antibodies or antigen-binding fragments thereof that specifically bind to human Flt-1 comprising one or more complementarity determining regions (CDR) selected from the group consisting of: a variable light (VL) chain CDR1 defined by an amino acid sequence having at least 80% identity to any one of SEQ ID NO:19 to SEQ ID NO:21, a VL CDR2 defined by an amino acid sequence having at least 80% identity to any one of SEQ ID NO:22 to SEQ ID NO:24; a VL CDR3 defined by an amino acid sequence having at least 80% identity to any one of SEQ ID NO:25 to SEQ ID NO:34; a variable heavy (VH) chain CDR1 defined by an amino acid sequence having at least 80% identity to any one of SEQ ID NO:1 to SEQ ID NO:4, a VH CDR2 defined by an amino acid sequence having at least 80% identity to any one of SEQ ID NO:5 to SEQ ID NO:14, and a VH CDR3 defined by an amino acid sequence having at least 80% identity to any one of SEQ ID NO:15 to SEQ ID NO:18.

In some embodiments, the one or more CDRs comprise the VL CDR3 defined by the amino acid sequence having at least 80% identity to any one of SEQ ID NO:25 to SEQ ID NO:34; and the VH CDR3 defined by the amino acid sequence having at least 80% identity to any one of SEQ ID NO:15 to SEQ ID NO:18.

In another embodiment, the one or more CDRs comprise the VL CDR1 defined by the amino acid sequence having at least 80% identity to any one of SEQ ID NO:19 to SEQ ID NO:21, the VL CDR2 defined by the amino acid sequence having at least 80% identity to any one of SEQ ID NO:22 to SEQ ID NO:24, and the VL CDR3 defined by the amino acid sequence having at least 80% identity to any one of SEQ ID NO:25 to SEQ ID NO:34. In a particular embodiment, VL chain comprises the VL CDR1, VL CDR2, and VL CDR3 defined by the amino acid sequence of SEQ ID NO:19, SEQ ID NO:22, and SEQ ID NO:25, respectively. In yet another embodiment, the VL chain comprises the VL CDR1, VL CDR2, and VL CDR3 defined by the amino acid sequence of SEQ ID NO:20, SEQ ID NO:23, and SEQ ID NO:25, respectively. In another embodiment, the VL chain comprises the VL CDR1 and VL CDR2 defined by the amino acid sequence of SEQ ID NO:21 and SEQ ID NO:24, respectively, and the VL CDR3 defined by the amino acid sequence of SEQ ID NO:26, SEQ ID NO:27, SEQ ID NO:28, SEQ ID NO:29, SEQ ID NO:30, SEQ ID NO:31, SEQ ID NO:32, SEQ ID NO:33, or SEQ ID NO:34. In a particular embodiment, the VL chain comprises the VL CDR1, VL CDR2, and VL CDR3 defined by the amino acid sequence of SEQ ID NO:21, SEQ ID NO:24, and SEQ ID NO:32, respectively.

In other embodiments, the one or more CDRs comprise the VH CDR1 defined by the amino acid sequence having at least 80% identity to any one of SEQ ID NO:1 to SEQ ID NO:4, the VH CDR2 defined by the amino acid sequence having at least 80% identity to any one of SEQ ID NO:5 to SEQ ID NO:14, and the VH CDR3 defined by the amino acid sequence having at least 80% identity to any one of SEQ ID NO:15 to SEQ ID NO:18. In a particular embodiment, the VH chain comprises the VH CDR1, VH CDR2, and VH CDR3 defined by the amino acid sequences of SEQ ID NO:1, SEQ ID NO:5, and SEQ ID NO:15, respectively. In another embodiment the VH chain comprises the VH CDR1, VH CDR2, and VH CDR3 defined by the amino acid sequences of SEQ ID NO:2, SEQ ID NO:6, and SEQ ID NO:16, respectively. In yet another embodiment, the VH chain comprises the VH CDR1, VH CDR2, and VH CDR3 defined by the amino acid sequences of SEQ ID NO:2, SEQ ID NO:10, and SEQ ID NO:18, respectively. In another embodiment, the VH chain comprises the VH CDR1 and the VH CDR3 defined by the amino acid sequences of SEQ ID NO:2 and SEQ ID NO:17, respectively, and the VH CDR2 defined by the amino acid sequence of SEQ ID NO:7, SEQ ID NO:8, SEQ ID NO:13 or SEQ ID NO:14. In another embodiment, the VH chain comprises the VH CDR1 and the VH CDR3 defined by the amino acid sequences of SEQ ID NO:3 and SEQ ID NO:17, respectively, and the VH CDR2 defined by the amino acid sequence of SEQ ID NO:9, SEQ ID NO:11 or SEQ ID NO:12. In yet another embodiment, the VH chain comprises the VH CDR1, VH CDR2, and VH CDR3 defined by the amino acid sequences of SEQ ID NO:4, SEQ ID NO:9, and SEQ ID NO:17, respectively. In a particular embodiment, the VH chain comprising the VH CDR1, VH CDR2, and VH CDR3 defined by the amino acid sequences of SEQ ID NO:3, SEQ ID NO:12, and SEQ ID NO:17, respectively.

In another aspect, the invention provides antibodies or antigen-binding fragments thereof that specifically bind to human Flt-1, comprising: (i) a light chain variable (VL) region comprising an amino acid sequence having at least 80% identity to any one of SEQ ID NO:49 to SEQ ID NO:61, and/or (ii) a heavy chain variable (VH) region comprising an amino acid sequence having at least 80% identity to any one of SEQ ID NO:35 to SEQ ID NO:48. In a particular embodiment the VL region comprises the amino acid sequence of SEQ ID NO:60 and the VH region comprises the amino acid sequence of SEQ ID NO:45.

In some embodiments the antibody further comprises a heavy chain constant region comprising an amino acid sequence having at least 80% identity to any one of SEQ ID NO:87 to SEQ ID NO:89.

In another aspect, the invention provides antibodies or antigen-binding fragments thereof that specifically binds to human Flt-1, comprising: (i) a light chain comprising an amino acid sequence having at least 80% identity to any one of SEQ ID NO:75 to SEQ ID NO:86, and/or (ii) a heavy chain comprising an amino acid sequence having at least 80% identity to any one of SEQ ID NO:62 to SEQ ID NO:74. In a particular embodiment, the light chain comprises the amino acid sequence of SEQ ID NO:76 and the heavy chain comprises the amino acid sequence of SEQ ID NO:71.

In another embodiment, the antibody or antigen-binding fragment thereof is selected from the group consisting of IgG, F(ab′)₂, F(ab)₂, Fab′, Fab, ScFvs, diabodies, triabodies and tetrabodies. In one embodiment the antibody or antigen-binding fragment thereof is IgG. In another embodiment the antibody or antigen-binding fragment thereof is IgGl. In yet another embodiment, the antibody or antigen-binding fragment thereof is a monoclonal antibody. In a particular embodiment, the antibody is a humanized monoclonal antibody. In yet another embodiment, the humanized monoclonal antibody contains a human Fc region. In some embodiments, Fc region contains one or more mutations that enhance the binding affinity between the Fc region and the FcRn receptor such that the in vivo half-life of the antibody is prolonged. In another embodiment, the Fc region contains one or more mutations at positions corresponding to Leu 234, Leu 235 and/or Gly 237 of human IgGl.

In one embodiment, the antibody or antigen-binding fragment thereof does not bind to VEGF R2 and/or VEGF R3. In another embodiment, the antibody or antigen-binding fragment thereof does not bind to a mouse or monkey Flt-1.

In another aspect, the invention provides an isolated antibody or antigen-binding fragment thereof that recognizes a peptide comprising an amino acid sequence corresponding to positions 139 to 148, positions 139 to 153, positions 178 to 206, positions 199 to 204 and positions 128 to 138 of SEQ ID NO:90, or a fragment thereof. In one embodiment the peptide consists of the amino acid sequence corresponding to positions 130 to 138, positions 141 to 148, positions 141 to 153 and positions 193 to 206 of SEQ ID NO:90.

In another aspect, the invention provides an isolated antibody or antigen-binding fragment thereof that competes with any anti-Flt-1 antibody or antigen-binding fragment thereof.

In another aspect, the invention provides pharmaceutical compositions comprising anti-Flt-1 antibodies or antigen-binding fragments thereof and a pharmaceutically acceptable carrier.

In yet another aspect, the invention provides polynucleotides encoding a CDR, a VL region, a VH region, a light chain, and/or a heavy chain of the antibody or antigen-binding fragment thereof of the invention. In one embodiment, the invention provides expression vectors comprising the polynucleotides. In yet another embodiment, the invention provides a host cell comprising the polynucleotide or the expression vector. In a particular embodiment, the invention provides methods of making an antibody or antigen-binding fragment thereof that specifically binds to human Flt-1 comprising culturing the host cell. In another embodiment, a hybridoma cell produces the antibody or antigen-binding fragment thereof.

In another aspect, the invention provides methods for treating a Flt-1-mediated disease, disorder or condition comprising administering to a subject in need of treatment an anti-Flt-1 antibody or antigen-binding fragment thereof. In a particular embodiment, the Flt-1-mediated disease, disorder or condition is Duchenne muscular dystrophy, Becker muscular dystrophy, bronchopulmonary dysplasia, preeclampsia or chronic kidney disease.

In another aspect, the method provides methods of treating Duchenne Muscular Dystrophy (DMD), the method comprising administering to a subject who is suffering from or susceptible to DMD an effective amount of an anti-Flt-1 antibody or antigen-binding fragment thereof, such that at least one symptom or feature of DMD is reduced in intensity, severity, or frequency, or has delayed onset. In one embodiment the method further comprises administering to the subject one or more additional therapeutic agents. In a particular embodiment the additional therapeutic agents are selected from the group consisting of prednisone, deflazacort, follistatin, RNA modulating therapeutics, exon-skipping therapeutics and gene therapy.

In one embodiment, the antibody or antigen-binding fragment thereof is administered parenterally. In some embodiments, the parenteral administration is selected from intravenous, intradermal, intrathecal, inhalation, transdermal (topical), intraocular, intramuscular, subcutaneous, and/or transmucosal administration. In a particular embodiment, the parenteral administration is intravenous administration. In yet another embodiment, the parenteral administration is subcutaneous administration.

In some embodiments, the antibody or antigen-binding fragment thereof is administered daily, twice weekly, weekly or monthly. In a particular embodiment antibody or antigen-binding fragment thereof is administered twice weekly.

In another embodiment, the effective amount of the antibody or antigen-binding fragment thereof is a dose amount of approximately 1 mg/kg to 50 mg/kg. In a particular embodiment the dose amount is approximately 1 mg/kg, 3 mg/kg or 10 mg/kg.

In one embodiment, the administration of the antibody or antigen-binding fragment thereof results in reduced fibrosis and/or necrosis relative to a control. In another embodiment, the administration of the antibody or antigen-binding fragment thereof results in improved angiogenesis in muscle of the subject relative to a control. In another embodiment the improved angiogenesis is reflected by increased blood flow on muscle pathology, increased VEGF levels in serum, decreased creatine kinase (CK) levels in serum, increased CD31 score by IHC, and/or reduced sFlt-1 levels in serum. In yet another embodiment, the administration of the antibody or antigen-binding fragment thereof results in improved muscle function relative to a control. In yet another embodiment, the improved muscle function is reflected by improved muscle force and/or resistance to fatigue.

In another aspect, the invention provides for a method of treating tissue fibrosis comprising administering to a subject in need of treatment an effective amount of an anti-Flt-1 antibody or antigen-binding fragment thereof.

BRIEF DESCRIPTION OF FIGURES

The present teachings described herein will be more fully understood from the following description of various illustrative embodiments, when read together with the accompanying drawings. It should be understood that the drawings described below are for illustration purposes only and are not intended to limit the scope of the present teachings in any way.

FIG. 1A shows exemplary results depicting clearance of anti-Flt-1 antibody 13B4 after mice were administered the antibody at a dose of 10 mg/kg intravenously.

FIG. 1B shows exemplary results depicting clearance of anti-Flt-1 antibody 10G12 after mice were administered the antibody at a dose of 10 mg/kg intravenously.

FIG. 2A shows exemplary results depicting peak serum anti-Flt-1 antibody levels. FIG. 2B shows exemplary results depicting trough serum anti-Flt-1 antibody levels.

FIG. 3 shows exemplary results depicting a decrease in free soluble Flt-1 (sFlt-1) levels in serum following administration of an anti-Flt-1 antibody (13B4 or 10G12), isotype control antibody, commercial antibody (Angio) or vehicle alone to mdx mice.

FIG. 4 shows exemplary results depicting an increase in serum VEGF levels following administration of an anti-Flt-1 antibody (13B4 or 10G12), isotype control antibody, commercial antibody (Angio) or vehicle alone to mdx mice.

FIGS. 5A-5D show exemplary results of CD31 staining of tissue sections obtained from the diaphragm muscle of mdv mice administered an anti-Flt-1 antibody (13B4 or 10G12), isotype control antibody or commercial antibody (Angio).

FIG. 6A shows exemplary results of quantification of the CD31 positive area as a percentage of the total stained area in tissue sections obtained from diaphragm muscle. FIG. 6B shows exemplary results of quantification of the CD31 positive area as a percentage of the total stained area in tissue sections obtained from the tibialis anterior (TA) muscle.

FIG. 6B shows exemplary results of quantification of the CD31 positive area as a percentage of the total stained area in tissue sections obtained from the tibialis anterior (TA) muscle of mdx mice administered an anti-Flt-1 antibody.

FIG. 7 shows exemplary results depicting binding of anti-Flt-1 antibodies to recombinant sFlt-1 by an ELISA assay.

FIG. 8 shows exemplary results depicting inhibition of binding of sFlt-1 to VEGF by anti-Flt-1 antibodies in a competition ELISA assay.

FIG. 9 shows exemplary results depicting rescue of phosphorylation of VEGF R2 by anti-Flt-1 antibodies. Human primary vein endothelial cells (HUVECs) were treated with VEGF in the presence of sFlt-1 and anti-Flt-1 antibodies and the level of VEGF R2 phosphorylation was determined. Percent rescue indicates the level of phosphorylation of VEGF R2 relative to the level of phosphorylation of VEGF R2 when HUVECs were treated with VEGF and sFlt-1 alone (i.e., no anti-Flt-1 antibody).

FIG. 10 shows exemplary results depicting inhibition of binding of soluble Flt-1 to VEGF by anti-Flt-1 antibodies in a competition ELISA assay.

FIG. 11 shows exemplary results depicting clearance of anti-Flt-1 antibodies from the serum over 672 hours after mice were administered the anti-Flt-1 antibody at a dose of 10 mg/kg intravenously.

FIGS. 12A-12C show exemplary results of CD31 staining of tissue sections from diaphragm muscle. FIGS. 12D-12F show exemplary results of CD31 staining of tissue sections obtained from tibialis anterior muscle.

FIGS. 13A-13C show exemplary biodistribution of anti-Flt-1 antibodies 27H9, 13B4 and 21B3 in the diaphragm, tibialis and gastrocnemius muscles of mice over a 256 hour time course following administration of the antibody.

FIG. 14A shows exemplary results depicting peak anti-Flt-1 antibody 21B3 levels at peak exposure. FIG. 14B shows exemplary results depicting trough anti-Flt-1 antibody 21B3 levels.

FIG. 15 shows exemplary results depicting free sFlt-1 following administration of anti-Flt-1 antibody 21B3 to mdx mice.

FIG. 16 shows exemplary results depicting VEGF levels following administration of anti-Flt-1 antibody 21B3 to mdx mice.

FIG. 17A-17E shows exemplary results of CD31 staining of tissue sections obtained from the diaphragm muscle of mdx mice administered anti-Flt-1 antibody 21B3 or isotype control antibody.

FIG. 18 shows exemplary results of quantification of the normalized CD31 positivity percentage in tissue sections obtained from the diaphragm muscle of mdx mice administered anti-Flt-1 antibody 21B3 or isotype control antibody.

FIG. 19A-19E shows exemplary results of CD31 staining of tissue sections obtained from the tibialis anterior muscle of mdx mice administered anti-Flt-1 antibody 21B3 or isotype control antibody.

FIG. 20 shows exemplary results of quantification of the normalized CD31 positivity percentage in tissue sections obtained from the tibialis anterior muscle of mdx mice administered anti-Flt-1 antibody 21B3 or isotype control antibody.

FIG. 21A shows exemplary results of reverse phase liquid chromatography/mass spectrometry (RP-LC/MS) analysis to determine the molecular weight of the deglycosylated 21B3 antibody. FIG. 21B shows exemplary results of analysis of the glycosylation pattern of the heavy chain.

FIGS. 22A and 22B show exemplary results depicting rescue of phosphorylation of VEGF R2 by anti-Flt-1 antibodies. Human primary vein endothelial cells (HUVECs) were treated with VEGF in the presence of sFlt-1 and anti-Flt-1 antibodies and the level of VEGF R2 phosphorylation was determined. Percent rescue indicates the level of phosphorylation of VEGF R2 relative to the level of phosphorylation of VEGF R2 when HUVECs were treated with VEGF and sFlt-1 alone (i.e., no anti-Flt-1 antibody).

FIG. 23 shows exemplary results depicting binding of anti-Flt-1 antibodies to recombinant sFlt-1 by an ELISA assay.

FIG. 24 shows exemplary results depicting serum levels of free anti-Flt-1 antibody 21B3 and isotype control antibody in mdx mice.

FIG. 25 shows exemplary results depicting serum levels of free sFlt-1 in mdx mice treated with either anti-Flt-1 antibody 21B3 or isotype control antibody.

FIG. 26 shows exemplary results depicting serum levels of VEGF in mdx mice treated with either anti-Flt-1 antibody 21B3 or isotype control antibody.

FIGS. 27A-2711 show exemplary results of CD31 staining of tissue sections obtained from the diaphragm muscle of mdx mice anti-Flt-1 antibody 21B3 or vehicle control for 6 (27A-27D) or 12 (27E-27H) weeks.

FIGS. 28A-28H show exemplary results of CD31 staining of tissue sections obtained from the gastrocnemius muscle of mdx mice administered anti-Flt-1 antibody 21B3 or vehicle control for 6 weeks (28A-28D) or 12 weeks (28E-28H).

FIGS. 29A-29H show exemplary results of CD31 staining of tissue sections obtained from the tibialis muscle of mdx mice administered anti-Flt-1 antibody 21B3 or vehicle control for 6 weeks (29A-29D) or 12 weeks (29E-29H).

FIGS. 30A-30C show exemplary results of quantification of the percent positivity of CD31 staining in tissue sections obtained from the diaphragm, gastrocnemius and tibialis muscle of mdx mice administered anti-Flt-1 antibody 21B3 or vehicle control antibody for 6 or 12 weeks.

FIGS. 31A-31H show exemplary results of collagen type I immunohistochemical staining of tissue sections obtained from the diaphragm muscle of mdx mice administered anti-Flt-1 antibody 21B3 or vehicle control for 6 weeks (31A-31D) or 12 weeks (31E-31H).

FIGS. 32A-32H show exemplary results of collagen type I immunohistochemical staining of tissue sections obtained from the gastrocnemius muscle of mdv mice administered anti-Flt-1 antibody 21B3 or vehicle control for 6 weeks (32A-32D) or 12 weeks (32E-32H).

FIGS. 33A-33H show exemplary results of collagen type I immunohistochemical staining of tissue sections obtained from the tibialis muscle of mdv mice administered anti-Flt-1 antibody 21B3 or vehicle control for 6 weeks (33A-33D) or 12 weeks (33E-33H).

FIGS. 34A-34C show exemplary results of quantification of the percent positivity of collagen type I staining in tissue sections obtained from the diaphragm, gastrocnemius and tibialis muscle of mdx mice administered anti-Flt-1 antibody 21B3 or vehicle control antibody for 6 or 12 weeks.

FIGS. 35A and 35B show exemplary results of quantification of the percent necrosis of gastrocnemius muscle of mdx mice administered anti-Flt-1 antibody 21B3 or vehicle control antibody for 6 or 12 weeks.

FIG. 36 shows exemplary results depicting a differential heat map comparing hydrogen/deuterium exchange of human sFlt-1 alone to that of human sFlt-1 and anti-Flt-1 antibody (21B3) mixture. Grey: no deuterium protection; blue: deuterium protection upon Fab binding.

FIG. 37 shows exemplary results depicting a differential heat map comparing hydrogen/deuterium exchange of human sFlt-1 alone to that of human sFlt-1 and anti-Flt-1 antibody (21C6) mixture. Grey: no deuterium protection; blue: deuterium protection upon Fab binding.

FIGS. 38A-38E show exemplary results depicting MS/MS spectra for identified peptides containing amino acid residues from epitope regions.

DEFINITIONS

In order for the present invention to be more readily understood, certain terms are first defined below. Additional definitions for the following terms and other terms are set forth throughout the specification.

Affinity: As is known in the art, “affinity” is a measure of the tightness with a particular ligand binds to its partner. In some embodiments, the ligand or partner is Flt-1. In some embodiments, the ligand or partner is soluble Flt-1. In some embodiments, the ligand or partner is a recombinant Flt-1. In a particular embodiment the ligand or partner is human sFlt-1. In a particular embodiment, the ligand or partner is a recombinant sFlt-1. In other embodiments, the ligand or partner is an anti-Flt-1 antibody. Affinities can be measured in different ways. In some embodiments, affinity is measured by a quantitative assay. In some such embodiments, binding partner concentration may be fixed to be in excess of ligand concentration so as to mimic physiological conditions. Alternatively or additionally, in some embodiments, binding partner concentration and/or ligand concentration may be varied. In some such embodiments, affinity may be compared to a reference under comparable conditions (e.g., concentrations).

Affinity matured (or affinity matured antibody): As used herein, the term “affinity matured” or “affinity matured antibody”, refers to an antibody with one or more alterations in one or more CDRs thereof which result an improvement in the affinity of the antibody for antigen, compared to a parent antibody which does not possess those alteration(s). In some embodiments, affinity matured antibodies will have nanomolar or even picomolar affinities for a target antigen. Affinity matured antibodies may be produced by any of a variety of procedures known in the art. Marks et al., BioTechnology 10:779-783 (1992) describes affinity maturation by V_(H) and V_(L) domain shuffling. Random mutagenesis of CDR and/or framework residues is described by: Barbas et al. Proc. Nat. Acad. Sci. U.S.A. 91:3809-3813 (1994); Schier et al., Gene 169: 147-155 (1995); Yelton et al., J. Immunol. 155: 1994-2004 (1995); Jackson et al., J. Immunol. 154(7):3310-9 (1995); and Hawkins et al., J. Mol. Biol. 226:889-896 (1992).

Amelioration: As used herein, the term “amelioration” is meant the prevention, reduction or palliation of a state, or improvement of the state of a subject. Amelioration includes, but does not require complete recovery or complete prevention of a disease condition.

Animal: As used herein, the term “animal” refers to any member of the animal kingdom. In some embodiments, “animal” refers to humans, at any stage of development. In some embodiments, “animal” refers to non-human animals, at any stage of development. In certain embodiments, the non-human animal is a mammal (e.g., a rodent, a mouse, a rat, a rabbit, a monkey, a dog, a cat, a sheep, cattle, a primate, and/or a pig). In some embodiments, animals include, but are not limited to, mammals, birds, reptiles, amphibians, fish, insects, and/or worms. In some embodiments, an animal may be a transgenic animal, genetically-engineered animal, and/or a clone.

Antibody: As used herein, the term “antibody” refers to any immunoglobulin, whether natural or wholly or partially synthetically produced. All derivatives thereof which maintain specific binding ability are also included in the term. The term also covers any protein having a binding domain which is homologous or largely homologous to an immunoglobulin-binding domain. Such proteins may be derived from natural sources, or partly or wholly synthetically produced. An antibody may be monoclonal or polyclonal. An antibody may be a member of any immunoglobulin isotype, including any of the human isotypes: IgG, IgM, IgA, IgD, and IgE. In certain embodiments, an antibody may be a member of the IgG immunoglobulin class (e.g., IgG1, IgG2, IgG3, etc). In some embodiments, an antibody may be a human antibody. In some embodiments, an antibody may be a humanized antibody.

As is known by those of ordinary skill in the art, antibodies produced in nature are typically comprised of four polypeptide chains, two heavy (H) chains and two light (L) chains interconnected by disulfide bonds. Each heavy and light chain is comprised of a variable region (abbreviated herein as HCVR, VH or V_(H) and LCVR, VL or V_(L), respectively) and a constant region. The constant region of a heavy chain comprises a C_(H)1, C_(H)2 and C_(H)3 domain (and optionally a C_(H)4 domain in the case of IgM and IgE). The constant region of a light chain is comprised of one domain, C_(L). The V_(H) and V_(L) regions further contain regions of hypervariability, termed complementarity determining regions (CDRs), interspersed with regions that are more conserved, which are termed framework regions (FR). Each V_(H) and V_(L) is composed of three CDRs and four FRs, arranged from amino-terminus to carboxy-terminus in the following order: FR1, CDR1, FR2, CDR2, FR3, CDR3, FR4. The binding regions of the heavy and light chains contain a binding domain that interacts with an antigen. The constant regions of the antibodies may mediate the binding of the immunoglobulin to host tissues or factors, including various cells of the immune system (e.g., effector cells) and the first component (C1q) of the classical complement system.

Antigen-binding portion: As used herein, the term “antigen-binding portion” or “antigen-binding fragment” refers to one or more fragments or portions of an antibody that retain the ability to specifically bind to an antigen (e.g., Flt-1). Examples of antigen-binding portions include (i) a Fab fragment, a monovalent fragment consisting of the V_(H), V_(L), C_(H)1 and C_(L) domains; (ii) a F(ab′)₂ fragment, a bivalent fragment comprising two Fab fragments linked by a disulfide bridge at the hinge region; (iii) a Fd fragment consisting of the V_(H) and C_(H)1 domains; (iv) a Fv fragment consisting of the V_(H) and V_(L) domains of a single arm of an antibody, (v) a dAb fragment (Ward et al., (1989) Nature 341:544-546), which comprises a single variable domain; (vi) an isolated complementarity determining region (CDR); (vii) a Fab′ fragment, which is essentially a Fab with part of the hinge region; (viii) a nanobody, a heavy chain variable region containing a single variable domain and two constant domains. Furthermore, although the two domains of the Fv fragment, V_(H) and V_(L), are coded for by separate genes, they can be joined, using recombinant methods, by a synthetic linker that enables them to be made as a single protein chain in which the V_(H) and V_(L) regions pair to form monovalent molecules (known as single chain Fv (scFv); see e.g., Bird et al. (1988) Science 242:423-426; and Huston et al. (1988) Proc. Natl. Acad. Sci. USA 85:5879-5883). An antigen-binding fragment of an antibody may optionally comprise a single chain antibody fragment. Alternatively or additionally, an antigen-binding fragment of an antibody may comprise multiple chains which are linked together, for example, by disulfide linkages. An antigen-binding fragment of an antibody may optionally comprise a multimolecular complex. A functional antibody fragment typically comprises at least about 50 amino acids and more typically comprises at least about 200 amino acids.

In some embodiments, an antibody fragment contains sufficient sequence of the parent antibody of which it is a fragment that it binds to the same antigen as does the parent antibody; in some embodiments, a fragment binds to the antigen with a comparable affinity to that of the parent antibody and/or competes with the parent antibody for binding to the antigen.

Those skilled in the art will appreciate that the term “antibody fragment” does not imply and is not restricted to any particular mode of generation. An antibody fragment may be produced through use of any appropriate methodology, including but not limited to cleavage of an intact antibody, chemical synthesis, and recombinant production. The fragments are screened for utility in the same manner as are intact antibodies.

Approximately or about: As used herein, the term “approximately” or “about,” as applied to one or more values of interest, refers to a value that is similar to a stated reference value. In certain embodiments, the term “approximately” or “about” refers to a range of values that fall within 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either direction (greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context (except where such number would exceed 100% of a possible value).

Associated with: Two events or entities are “associated” with one another, as that term is used herein, if the presence, level and/or form of one is correlated with that of the other. For example, a particular entity (e.g., polypeptide) is considered to be associated with a particular disease, disorder, or condition, if its presence, level and/or form correlates with incidence of and/or susceptibility to the disease, disorder, or condition (e.g., across a relevant population). In some embodiments, two or more entities are physically “associated” with one another if they interact, directly or indirectly, so that they are and remain in physical proximity with one another. In some embodiments, two or more entities that are physically associated with one another are covalently linked to one another; in some embodiments, two or more entities that are physically associated with one another are not covalently linked to one another but are non-covalently associated, for example by means of hydrogen bonds, van der Waals interaction, hydrophobic interactions, magnetism, and combinations thereof.

Carrier or diluent: As used herein, the terms “carrier” and “diluent” refer to a pharmaceutically acceptable (e.g., safe and non-toxic for administration to a human) carrier or diluting substance useful for the preparation of a pharmaceutical formulation. Exemplary diluents include sterile water, bacteriostatic water for injection (BWFI), a pH buffered solution (e.g. phosphate-buffered saline), sterile saline solution, Ringer's solution or dextrose solution.

CDR: As used herein, refers to a complementarity determining region within an antibody variable region. There are three CDRs in each of the variable regions of the heavy chain and the light chain, which are designated CDR1, CDR2 and CDR3, for each of the variable regions. A “set of CDRs” or “CDR set” refers to a group of three or six CDRs that occur in either a single variable region capable of binding the antigen or the CDRs of cognate heavy and light chain variable regions capable of binding the antigen. Certain systems have been established in the art for defining CDR boundaries (e.g., Kabat, Chothia, etc.); those skilled in the art appreciate the differences between and among these systems and are capable of understanding CDR boundaries to the extent required to understand and to practice the claimed invention.

Chimeric antibody: as used herein, refers to an antibody whose amino acid sequence includes V_(H) and V_(L) region sequences that are found in a first species and constant region sequences that are found in a second species, different from the first species. In many embodiments, a chimeric antibody has murine V_(H) and V_(L) regions linked to human constant regions. In some embodiments, an antibody with human V_(H) and V_(L) regions linked to non-human constant regions (e.g., a mouse constant region) is referred to as a “reverse chimeric antibody.”

Dosage form: As used herein, the terms “dosage form” and “unit dosage form” refer to a physically discrete unit of a therapeutic protein (e.g., antibody) for the patient to be treated. Each unit contains a predetermined quantity of active material calculated to produce the desired therapeutic effect. It will be understood, however, that the total dosage of the composition will be decided by the attending physician within the scope of sound medical judgment.

Dysfunction: As used herein, the term “dysfunction” refers to an abnormal function. Dysfunction of a molecule (e.g., a protein) can be caused by an increase or decrease of an activity associated with such molecule. Dysfunction of a molecule can be caused by defects associated with the molecule itself or other molecules that directly or indirectly interact with or regulate the molecule.

Epitope: as used herein, includes any moiety that is specifically recognized by an immunoglobulin (e.g., antibody, antibody fragment thereof, receptor) binding component. In some embodiments, an epitope is comprised of a plurality of chemical atoms or groups on an antigen. In some embodiments, such chemical atoms or groups are surface-exposed when the antigen adopts a relevant three-dimensional conformation. In some embodiments, such chemical atoms or groups are physically near to each other in space when the antigen adopts such a conformation. In some embodiments, at least some such chemical atoms are groups are physically separated from one another when the antigen adopts an alternative conformation (e.g., is linearized).

Fc region: As used herein, the term “Fc region” refers to a dimer of two “Fc polypeptides”, each “Fc polypeptide” comprising the constant region of an antibody excluding the first constant region immunoglobulin domain. In some embodiments, an “Fc region” includes two Fc polypeptides linked by one or more disulfide bonds, chemical linkers, or peptide linkers. “Fc polypeptide” refers to the last two constant region immunoglobulin domains of IgA, IgD, and IgG, and the last three constant region immunoglobulin domains of IgE and IgM, and may also include part or all of the flexible hinge N-terminal to these domains. For IgG, “Fc polypeptide” comprises immunoglobulin domains Cgamma2 (Cγ2) and Cgamma3 (Cγ3) and the lower part of the hinge between Cgamma1 (Cγ1) and Cγ2. Although the boundaries of the Fc polypeptide may vary, the human IgG heavy chain Fc polypeptide is usually defined to comprise residues starting at T223 or C226 or P230, to its carboxyl-terminus, wherein the numbering is according to the EU index as in Kabat et al. (1991, NIH Publication 91-3242, National Technical Information Services, Springfield, Va.). For IgA, Fc polypeptide comprises immunoglobulin domains Calpha2 (Cα2) and Calpha3 (Cα3) and the lower part of the hinge between Calpha1 (Cα1) and Cα2. An Fc region can be synthetic, recombinant, or generated from natural sources such as IVIG.

Framework or framework region: As used herein, refers to the sequences of a variable region minus the CDRs. Because a CDR sequence can be determined by different systems, likewise a framework sequence is subject to correspondingly different interpretations. The six CDRs divide the framework regions on the heavy and light chains into four sub-regions (FR1, FR2, FR3 and FR4) on each chain, in which CDR1 is positioned between FR1 and FR2, CDR2 between FR2 and FR3, and CDR3 between FR3 and FR4. Without specifying the particular sub-regions as FR1, FR2, FR3 or FR4, a framework region, as referred by others, represents the combined FRs within the variable region of a single, naturally occurring immunoglobulin chain. As used herein, a FR represents one of the four sub-regions, FR1, for example, represents the first framework region closest to the amino terminal end of the variable region and 5′ with respect to CDR1, and FRs represents two or more of the sub-regions constituting a framework region.

Half-Life: As used herein, the term “half-life” is the time required for a quantity such as protein concentration or activity to fall to half of its value as measured at the beginning of a time period.

High affinity: As used herein, the term “high affinity”, when referring an IgG type antibody, refers to an antibody having a K_(D) of 10⁻⁸M or less, more preferably 10⁻⁹ M or less and even more preferably 10⁻¹⁰ M or less for a domain of Flt-1. However, “high affinity” binding can vary for other antibody isotypes. For example, “high affinity” binding for an IgM isotype refers to an antibody having a K_(D) of 10⁻⁷ M or less, more preferably 10⁻⁸ M or less, even more preferably 10⁻⁹ M or less.

Human antibody: As used herein, is intended to include antibodies having variable and constant regions generated (or assembled) from human immunoglobulin sequences. In some embodiments, antibodies (or antibody components) may be considered to be “human” even though their amino acid sequences include residues or elements not encoded by human germline immunoglobulin sequences (e.g., include sequence variations, for example that may (originally) have been introduced by random or site-specific mutagenesis in vitro or by somatic mutation in vivo), for example in one or more CDRs and in particular CDR3.

Human monoclonal antibody: As used herein, is intended to refer to antibodies displaying a single binding specificity which have variable regions in which both the framework and CDR regions are derived from human germline immunoglobulin sequences. In one embodiment, the human monoclonal antibodies are produced by a hybridoma which includes a B cell obtained from a transgenic nonhuman animal, e.g., a transgenic mouse, having a genome comprising a human heave chain transgene and a light chain transgene fused to an immortalized cell.

Humanized: As is known in the art, the term “humanized” is commonly used to refer to antibodies (or antibody components) whose amino acid sequence includes V_(H) and V_(L) region sequences from a reference antibody raised in a non-human species (e.g., a mouse, a llama), but also includes modifications in those sequences relative to the reference antibody intended to render them more “human-like”, i.e., more similar to human germline variable sequences. In some embodiments, a “humanized” antibody (or antibody component) is one that immunospecifically binds to an antigen of interest and that has a framework (FR) region having substantially the amino acid sequence as that of a human antibody, and a complementary determining region (CDR) having substantially the amino acid sequence as that of a non-human antibody (e.g., a mouse, a llama). A humanized antibody comprises substantially all of at least one, and typically two, variable domains (Fab, Fab′, F(ab′)₂, FabC, Fv) in which all or substantially all of the CDR regions correspond to those of a non-human immunoglobulin (i.e., donor immunoglobulin) and all or substantially all of the framework regions are those of a human immunoglobulin consensus sequence. In some embodiments, a humanized antibody also comprises at least a portion of an immunoglobulin constant region (Fc), typically that of a human immunoglobulin constant region. In some embodiments, a humanized antibody contains both the light chain as well as at least the variable domain of a heavy chain. The antibody also may include a C_(H)1, hinge, C_(H)2, C_(H)3, and, optionally, a C_(H)4 region of a heavy chain constant region. In some embodiments, a humanized antibody only contains a humanized V_(L) region. In some embodiments, a humanized antibody only contains a humanized V_(H) region. In some certain embodiments, a humanized antibody contains humanized V_(H) and V_(L) regions.

Hypertrophy: As used herein, the term “hypertrophy” refers to the increase in volume of an organ or tissue due to the enlargement of its component cells.

Improve, increase, or reduce: As used herein, the terms “improve,” “increase” or “reduce,” or grammatical equivalents, indicate values that are relative to a baseline measurement, such as a measurement in the same individual prior to initiation of the treatment described herein, or a measurement in a control individual (or multiple control individuals) in the absence of the treatment described herein. A “control individual” is an individual afflicted with the same form of disease as the individual being treated, who is about the same age as the individual being treated (to ensure that the stages of the disease in the treated individual and the control individual(s) are comparable).

Inhibition: As used herein, the terms “inhibition,” “inhibit” and “inhibiting” refer to processes or methods of decreasing or reducing activity and/or expression of a protein or a gene of interest. Typically, inhibiting a protein or a gene refers to reducing expression or a relevant activity of the protein or gene by at least 10% or more, for example, 20%, 30%, 40%, or 50%, 60%, 70%, 80%, 90% or more, or a decrease in expression or the relevant activity of greater than 1-fold, 2-fold, 3-fold, 4-fold, 5-fold, 10-fold, 50-fold, 100-fold or more as measured by one or more methods described herein or recognized in the art.

In Vitro: As used herein, the term “in vitro” refers to events that occur in an artificial environment, e.g., in a test tube or reaction vessel, in cell culture, etc., rather than within a multi-cellular organism.

In Vivo: As used herein, the term “in vivo” refers to events that occur within a multi-cellular organism, such as a human and a non-human animal. In the context of cell-based systems, the term may be used to refer to events that occur within a living cell (as opposed to, for example, in vitro systems).

Isolated Antibody: As used herein, the term “isolated antibody” is intended to refer to an antibody that is substantially free of other antibodies having different antigenic specificities (e.g., an isolated antibody that specifically binds to Flt-1). Moreover, an isolated antibody may be substantially free of other cellular material and/or chemicals.

K_(a): As used herein, refers to the association rate of a particular antibody-antigen interaction, whereas the term “K_(d),” as used herein, is intended to refer to the dissociation rate of a particular antibody-antigen interaction. The term “K_(D)”, as used herein, is intended to refer to the dissociation constant, which is obtained from the ratio of Kd to Ka (i.e., Kd/Ka) and is expressed as a molar concentration (M). K_(D) values for antibodies can be determined using methods well established in the art. A preferred method for determining the K_(D) of an antibody is by using surface plasmon resonance, preferably using a biosensor system such as a BIAcore® system.

Light-chain reshuffling: As used herein, the term “light-chain reshuffling” is intended to refer to an affinity maturation step where the heavy chain sequence is kept constant and a library of light chain sequences is generated. The light chain library is screened against the heavy chain to identify antibodies with improved binding affinity. The improved binding affinity may be in the nanomolar or picomolar ranges.

Monoclonal antibody: As used herein, the term “monoclonal antibody” is intended to refer to a preparation of antibody molecules of a single molecular composition. A monoclonal antibody composition displays a single binding specificity and affinity for a particular epitope.

Pharmaceutically acceptable: As used herein, the term “pharmaceutically acceptable” refers to substances that, within the scope of sound medical judgment, are suitable for use in contact with the tissues of human beings and animals without excessive toxicity, irritation, allergic response, or other problem or complication, commensurate with a reasonable benefit/risk ratio.

Polypeptide: As used herein, the term “polypeptide” refers to a sequential chain of amino acids linked together via peptide bonds. The term is used to refer to an amino acid chain of any length, but one of ordinary skill in the art will understand that the term is not limited to lengthy chains and can refer to a minimal chain comprising two amino acids linked together via a peptide bond. As is known to those skilled in the art, polypeptides may be processed and/or modified.

Prevent: As used herein, the term “prevent” or “prevention”, when used in connection with the occurrence of a disease, disorder, and/or condition, refers to reducing the risk of developing the disease, disorder and/or condition. See the definition of “risk.”

Protein: As used herein, the term “protein” refers to one or more polypeptides that function as a discrete unit. If a single polypeptide is the discrete functioning unit and does not require permanent or temporary physical association with other polypeptides in order to form the discrete functioning unit, the terms “polypeptide” and “protein” may be used interchangeably. If the discrete functional unit is comprised of more than one polypeptide that physically associate with one another, the term “protein” refers to the multiple polypeptides that are physically coupled and function together as the discrete unit.

Risk: As will be understood from context, a “risk” of a disease, disorder, and/or condition comprises a likelihood that a particular individual will develop a disease, disorder, and/or condition (e.g., DMD). In some embodiments, risk is expressed as a percentage. In some embodiments, risk is from 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90 up to 100%. In some embodiments risk is expressed as a risk relative to a risk associated with a reference sample or group of reference samples. In some embodiments, a reference sample or group of reference samples have a known risk of a disease, disorder, condition and/or event (e.g., DMD). In some embodiments a reference sample or group of reference samples are from individuals comparable to a particular individual. In some embodiments, relative risk is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more.

Selective binding: As used herein, “selective binding”, “selectively binds” “specific binding”, or “specifically binds” refers, with respect to a binding moiety and a target, preferential association of a binding moiety to a target and not to an entity that is not the target. A certain degree of non-specific binding may occur between a binding moiety and a non-target. In some embodiments, a binding moiety selectively binds a target if binding between the binding moiety and the target is greater than 2-fold, greater than 5-fold, greater than 10-fold, or greater than 100-fold as compared with binding of the binding moiety and a non-target. In some embodiments, a binding moiety selectively binds a target if the binding affinity is less than about 10⁻⁵M, less than about 10⁻⁶ M, less than about 10⁻⁷ M, less than about 10⁻⁸M, or less than about 10⁻⁹M.

Striated muscle: As used herein, the term “striated muscle” refers to multinucleated muscle tissue with regular arrangement of their intracellular contractile units, sarcomeres, leading to the appearance of striations using microscopy and under voluntary control. Typically, striated muscle can be cardiac muscle, skeletal muscle, and Branchiomeric muscles.

Smooth muscle: As used herein, the term “smooth muscle” refers to involuntarily controlled, non-striated muscle, including unitary and multi-unit muscle.

Subject: As used herein, the term “subject” refers to a human or any non-human animal (e.g., mouse, rat, rabbit, dog, cat, cattle, swine, sheep, horse or primate). A human includes pre- and post-natal forms. In many embodiments, a subject is a human being. A subject can be a patient, which refers to a human presenting to a medical provider for diagnosis or treatment of a disease. The term “subject” is used herein interchangeably with “individual” or “patient.” A subject can be afflicted with or susceptible to a disease or disorder but may or may not display symptoms of the disease or disorder.

Substantially: As used herein, the term “substantially” refers to the qualitative condition of exhibiting total or near-total extent or degree of a characteristic or property of interest. One of ordinary skill in the biological arts will understand that biological and chemical phenomena rarely, if ever, go to completion and/or proceed to completeness or achieve or avoid an absolute result. The term “substantially” is therefore used herein to capture the potential lack of completeness inherent in many biological and chemical phenomena.

Substantial homology: The phrase “substantial homology” is used herein to refer to a comparison between amino acid or nucleic acid sequences. As will be appreciated by those of ordinary skill in the art, two sequences are generally considered to be “substantially homologous” if they contain homologous residues in corresponding positions. Homologous residues may be identical residues. Alternatively, homologous residues may be non-identical residues will appropriately similar structural and/or functional characteristics. For example, as is well known by those of ordinary skill in the art, certain amino acids are typically classified as “hydrophobic” or “hydrophilic” amino acids, and/or as having “polar” or “non-polar” side chains. Substitution of one amino acid for another of the same type may often be considered a “homologous” substitution.

As is well known in this art, amino acid or nucleic acid sequences may be compared using any of a variety of algorithms, including those available in commercial computer programs such as BLASTN for nucleotide sequences and BLASTP, gapped BLAST, and PSI-BLAST for amino acid sequences. Exemplary such programs are described in Altschul, et al., basic local alignment search tool, J. Mol. Biol., 215(3): 403-410, 1990; Altschul, et al., Methods in Enzymology; Altschul, et al., “Gapped BLAST and PSI-BLAST: a new generation of protein database search programs”, Nucleic Acids Res. 25:3389-3402, 1997; Baxevanis, et al., Bioinformatics: A Practical Guide to the Analysis of Genes and Proteins, Wiley, 1998; and Misener, et al., (eds.), Bioinformatics Methods and Protocols (Methods in Molecular Biology, Vol. 132), Humana Press, 1999. In addition to identifying homologous sequences, the programs mentioned above typically provide an indication of the degree of homology. In some embodiments, two sequences are considered to be substantially homologous if at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more of their corresponding residues are homologous over a relevant stretch of residues. In some embodiments, the relevant stretch is a complete sequence. In some embodiments, the relevant stretch is at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, 500 or more residues.

Substantial identity: The phrase “substantial identity” is used herein to refer to a comparison between amino acid or nucleic acid sequences. As will be appreciated by those of ordinary skill in the art, two sequences are generally considered to be “substantially identical” if they contain identical residues in corresponding positions. As is well known in this art, amino acid or nucleic acid sequences may be compared using any of a variety of algorithms, including those available in commercial computer programs such as BLASTN for nucleotide sequences and BLASTP, gapped BLAST, and PSI-BLAST for amino acid sequences. Exemplary such programs are described in Altschul, et al., Basic local alignment search tool, J. Mol. Biol., 215(3): 403-410, 1990; Altschul, et al., Methods in Enzymology; Altschul et al., Nucleic Acids Res. 25:3389-3402, 1997; Baxevanis et al., Bioinformatics: A Practical Guide to the Analysis of Genes and Proteins, Wiley, 1998; and Misener, et al., (eds.), Bioinformatics Methods and Protocols (Methods in Molecular Biology, Vol. 132), Humana Press, 1999. In addition to identifying identical sequences, the programs mentioned above typically provide an indication of the degree of identity. In some embodiments, two sequences are considered to be substantially identical if at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more of their corresponding residues are identical over a relevant stretch of residues. In some embodiments, the relevant stretch is a complete sequence. In some embodiments, the relevant stretch is at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, 500 or more residues.

Surface plasmon resonance: as used herein, refers to an optical phenomenon that allows for the analysis of specific binding interactions in real-time, for example through detection of alterations in protein concentrations within a biosensor matrix, such as by using a Biacore system (Pharmacia Biosensor AB, Uppsala, Sweden and Piscataway, N.J.). For further descriptions, see Jonsson, U., et al. (1993) Ann. Biol. Clin. 51: 19-26; Jonsson, U., et al. (1991) Biotechniques 11:620-627; Johnsson, B., et al. (1995) J. Mol. Recognit. 8: 125-131; and Johnnson, B., et al. (1991) Anal. Biochem. 198:268-277.

Suffering from: An individual who is “suffering from” a disease, disorder, and/or condition has been diagnosed with or displays one or more symptoms of the disease, disorder, and/or condition such as, for example DMD.

Susceptible to: An individual who is “susceptible to” a disease, disorder, and/or condition has not been diagnosed with the disease, disorder, and/or condition. In some embodiments, an individual who is susceptible to a disease, disorder, and/or condition may not exhibit symptoms of the disease, disorder, and/or condition. In some embodiments, an individual who is susceptible to a disease, disorder, condition, or event (for example, DMD) may be characterized by one or more of the following: (1) a genetic mutation associated with development of the disease, disorder, and/or condition; (2) a genetic polymorphism associated with development of the disease, disorder, and/or condition; (3) increased and/or decreased expression and/or activity of a protein associated with the disease, disorder, and/or condition; (4) habits and/or lifestyles associated with development of the disease, disorder, condition, and/or event (5) having undergone, planning to undergo, or requiring a transplant. In some embodiments, an individual who is susceptible to a disease, disorder, and/or condition will develop the disease, disorder, and/or condition. In some embodiments, an individual who is susceptible to a disease, disorder, and/or condition will not develop the disease, disorder, and/or condition.

Target tissues: As used herein, the term “target tissues” refers to any tissue that is affected by a disease to be treated such as DMD. In some embodiments, target tissues include those tissues that display disease-associated pathology, symptom, or feature, including but not limited to muscle wasting, skeletal deformation, cardiomyopathy, muscle ischemia, cognitive impairment, and impaired respiratory function. In some embodiment the target tissue is smooth muscle, striated muscle or cardiac muscle.

Therapeutically effective amount: As used herein, the term “therapeutically effective amount” of a therapeutic agent means an amount that is sufficient, when administered to a subject suffering from or susceptible to a disease, disorder, and/or condition, to treat, diagnose, prevent, and/or delay the onset of the symptom(s) of the disease, disorder, and/or condition. It will be appreciated by those of ordinary skill in the art that a therapeutically effective amount is typically administered via a dosing regimen comprising at least one unit dose.

Treating: As used herein, the term “treat,” “treatment,” or “treating” refers to any method used to partially or completely alleviate, ameliorate, relieve, inhibit, prevent, delay onset of, reduce severity of and/or reduce incidence of one or more symptoms or features of a particular disease, disorder, and/or condition, such as for example, DMD. Treatment may be administered to a subject who does not exhibit signs of a disease and/or exhibits only early signs of the disease for the purpose of decreasing the risk of developing pathology associated with the disease.

DETAILED DESCRIPTION

The present invention provides, among other things, methods and compositions for treating muscular dystrophy, including Duchenne muscular dystrophy (DMD) and/or Becker Muscular Dystrophy, based on the use of anti-Flt-1 antibodies, or antigen-binding fragments thereof, as therapeutics for treating muscular dystrophy. In some embodiments, the present invention provides methods of treating DMD including administering to an individual who is suffering from or susceptible to DMD a therapeutically effective amount of an anti-Flt-1 antibody, or antigen-binding fragment thereof, such that at least one symptom or feature of DMD is reduced in intensity, severity, or frequency, or has delayed onset.

Various aspects of the invention are described in detail in the following sections. The use of sections is not meant to limit the invention. Each section can apply to any aspect of the invention. In this application, the use of “or” means “and/or” unless stated otherwise.

Duchenne Muscular Dystrophy (DMD)

DMD is a disease characterized by progressive deterioration of muscles and loss of muscle related functions throughout the body. It is contemplated that the present invention provides methods and compositions for slowing, delaying or preventing deterioration of muscles, regenerating muscle and reversing, eliminating, delaying, preventing, or minimizing fibrosis, inflammation and other symptoms or features associated with DMD and other muscular dystrophies in various muscle tissues.

Muscle Tissues

There are two major types of muscle tissue in an animal, striated muscle and smooth muscle. As used herein, the term “striated muscle” refers to muscle tissues containing repeating sarcomeres. Striated muscle tends to be under voluntary control and attached to the skeleton. Striated muscle allows for voluntary movement of the body and includes the major muscle groups including the quadriceps, gastrocnemius, biceps, triceps, trapezius, deltoids, and many others. Striated muscle tends to be very long and, many striated muscles are able to function independently. Some striated muscle, however, is not attached to the skeleton, including those in the mouth, anus, heart, and upper portion of the esophagus.

Smooth muscle, on the other hand, has very different structure. Rather than a series of long muscles with separate skeletal attachments, smooth muscle tends to be organized into continuous sheets with mechanical linkages between smooth muscle cells. Smooth muscle is often located in the walls of hollow organs and is usually not under voluntary control. Smooth muscles lining a particular organ must bear the same load and contract concurrently. Smooth muscle functions, at least in part, to handle changes in load on hollow organs caused by movement and/or changes in posture or pressure. This dual role means that smooth muscle must not only be able to contract like striated muscle, but also that it must be able to contract tonically to maintain organ dimensions against sustained loads. Examples of smooth muscles are those lining blood vessels, bronchioles, bladder, and gastrointestinal tract such as rectum.

The strength of a muscle depends on the number and sizes of the muscle's cells and on their anatomic arrangement. Increasing the diameter of a muscle fiber either by synthesis of new myofibrils (hypertrophy) and/or the formation of more muscle cells (hyperplasia) will increase the force-generating capacity of the muscle.

Muscles may also be grouped by location or function. In some embodiments, an Flt-1 antibody or antigen-binding fragment thereof is targeted to one or more muscles of the face, one or more muscles for mastication, one or more muscles of the tongue and neck, one or more muscles of the thorax, one or more muscles of the pectoral girdle and arms, one or more muscles of the arm and shoulder, one or more ventral and dorsal forearm muscles, one or more muscles of the hand, one or more muscles of the erector spinae, one or more muscles of the pelvic girdle and legs, and/or one or more muscles of the foreleg and foot.

In some embodiments, muscles of the face include, but are not limited to, intraocular muscles such as ciliary, iris dilator, iris sphincter; muscles of the ear such as auriculares, temporoparietalis, stapedius, tensor tympani; muscles of the nose such as procerus, nasalis, dilator naris, depressor septi nasi, levator labii superioris alaeque nasi; muscles of the mouth such as levator anguli oris, depressor anguli oris, orbicularis oris, Buccinator, Zygomaticus Major and Minor, Platysma, Levator Labii Superioris, Depressor Labii Inferioris, Risorius, Mentalis, and/or Corrugator Supercilii.

In some embodiments, muscles of mastication include, but are not limited to, Masseter, Temporalis, Medial Pterygoid, Lateral Pterygoid. In some embodiments, muscles of the tongue and neck include, but are not limited to, Genioglossus, Styloglossus, Palatoglossus, Hyoglossus, Digastric, Stylohyoid, Mylohyoid, Geniohyoid, Omohyoid, Sternohyoid, Sternothyroid, Thyrohyoid, Sternocleidomastoid, Anterior Scalene, Middle Scalene, and/or Posterior Scalene.

In some embodiments, muscles of the thorax, pectoral girdle, and arms include, but are not limited to, Subclavius Pectoralis major, Pectoralis minor, Rectus abdominis, External abdominal oblique, Internal abdominal oblique, Transversus Abdominis, Diaphragm, External Intercostals, Internal Intercostals, Serratus Anterior, Trapezius, Levator Scapulae, Rhomboideus Major, Rhomboideus Minor, Latissimus dorsi, Deltoid, subscapularis, supraspinatus, infraspinatus, Teres major, Teres minor, and/or Coracobrachialis.

In some embodiments, muscles of the arm and shoulder include, but are not limited to, Biceps brachii-Long Head, Biceps brachii-Short Head, Triceps brachii-Long Head, Triceps brachii Lateral Head, Triceps brachii-Medial Head, Anconeus, Pronator teres, Supinator, and/or Brachialis.

In some embodiments, muscles of the ventral and dorsal forearm include, but are not limited to, Brachioradialis, Flexor carpi radialis, Flexor carpi ulnaris, Palmaris longus, Extensor carpi ulnaris, Extensor carpi radialis longus, Extensor carpi radialis brevis, Extensor digitorum, Extensor digiti minimi.

In some embodiments, muscles of the hand include, but are not limited to intrinsic muscles of the hand such as thenar, abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, hypothenar, abductor digiti minimi, the flexor digiti minimi brevis, opponens digiti minimi, palmar interossei, dorsal interossei and/or lumbricals.

In some embodiments, muscles of the erector spinae include, but are not limited to, cervicalis, spinalis, longissimus, and/or iliocostalis.

In some embodiments, muscles of the pelvic girdle and the legs include, but are not limited to, Psoas Major, Iliacus, quadratus femoris, Adductor longus, Adductor brevis, Adductor magnus, Gracilis, Sartorius, Quadriceps femoris such as, rectus femoris, vastus lateralis, vastus medialis, vastus intermedius, Gastrocnemius, Fibularis (Peroneus) Longus, Soleus, Gluteus maximus, Gluteus medius, Gluteus minimus, Hamstrings: Biceps Femoris: Long Head, Hamstrings: Biceps Femoris: Short Head, Hamstrings: Semitendinosus, Hamstrings: Semimembranosus, Tensor fasciae latae, Pectineus, and/or Tibialis anterior.

In some embodiments, muscles of the foreleg and foot include, but are not limited to, Extensor digitorum longus, Extensor hallucis longus, peroneus brevis, plantaris, Tibialis posterior, Flexor hallucis longus, extensor digitorum brevis, extensor hallucis brevis, Abductor hallucis, flexor hallucis brevis, Abductor digiti minimi, flexor digiti minimi, opponens digiti minimi, extensor digitorum brevis, lumbricales of the foot, Quadratus plantae or flexor accessorius, flexor digitorum brevis, dorsal interossei, and/or plantar interossei.

Exemplary muscle targets are summarized in Table 1.

TABLE 1 ORBICULARIS OCULI Intraocular: ciliary, iris dilator, iris sphincter Ear: auriculares, temporoparietalis, stapedius, tensor tympani Nose: procerus, nasalis, dilator naris, depressor septi nasi, levator labii superioris alaeque nasi Mouth: levator anguli oris, depressor anguli oris, orbicularis oris Buccinator Zygomaticus Major Platysma Levator Labii and Minor Superioris Depressor Labii Risorius Mentalis Corrugator Supercilii Inferioris Anconeus Pronator teres Supinator Brachialis MUSCLES OF MASTICATON Masseter Temporalis Medial Pterygoid Lateral Pterygoid MUSCLES OF THE TONGUE AND NECK Genioglossus Styloglossus Palatoglossus Hyoglossus Digastric Stylohyoid Mylohyoid Geniohyoid Omohyoid Sternohyoid Sternothyroid Thyrohyoid Sternocleidomastoid Anterior Scalene Middle Scalene Posterior Scalene MUSCLES OF THE THORAX, PECTORAL GIRDLE AND ARMS Subclavius Pectoralis major Pectoralis minor Rectus abdominis External abdominal Internal abdominal Transversus Diaphragm oblique oblique Abdominis External Intercostals Internal Intercostals Serratus Anterior Trapezius Levator Scapulae Rhomboideus Major Rhomboideus Minor Latissimus dorsi Deltoid subscapularis supraspinatus infraspinatus Teres major Teres minor Coracobrachialis ARM AND SHOULDER Biceps brachii-Long Biceps brachii-Short Triceps brachii-Long Triceps brachii-Lateral Head Head Head Head Triceps brachii-Medial Anconeus Pronator teres Supinator Head Brachialis FOREARM MUSCLES: Ventral and Dorsal Brachioradialis Flexor carpi radialis Flexor carpi ulnaris Palmaris longus Extensor carpi ulnaris Extensor carpi Extensor carpi Extensor digitorum radialis longus radialis brevis Extensor digiti minimi erector spinae: erector spinae: erector spinae: cervicalis spinalis longissimus erector spinae: iliocostalis Intrinsic Muscles of the Hand: thenar, abductor pollicis brevis, flexor pollicis brevis, and the opponens pollicis Intrinsic Muscles of the Hand: hypothenar, abductor digiti minimi, the flexor digiti minimi brevis, and the opponens digiti minimi Intrinsic Muscles of the Hand: palmar interossei, dorsal interossei and lumbricals MUSCLES OF THE PELVIC GIRDLE AND THE LEGS Iliopsoas: Psoas Major Iliopsoas: Iliacus quadratus femoris Adductor longus Adductor brevis Adductor magnus Gracilis Sartorius Quadriceps femoris: Quadriceps femoris: Quadriceps femoris: Quadriceps femoris: rectus femoris vastus lateralis vastus medialis vastus intermedius Gastrocnemius Fibularis (Peroneus) Soleus Gluteus maximus Longus Gluteus medius Gluteus minimus Hamstrings: Biceps Hamstrings: Biceps Femoris: Long Head Femoris: Short Head Hamstrings: Hamstrings: Tensor fasciae latae Pectineus Semitendinosus Semimembranosus Tibialis anterior MUSCLES OF THE FORELEG AND FOOT Extensor digitorum Extensor hallucis peroneus brevis plantaris longus longus Tibialis posterior Flexor hallucis longus extensor digitorum extensor hallucis brevis brevis Abductor hallucis flexor hallucis brevis Abductor digiti minimi flexor digiti minimi opponens digiti minimi extensor digitorum lumbricales of the Quadratus plantae brevis foot or flexor accessorius Flexor digitorum brevis dorsal interossei plantar interossei

Muscular Dystrophy

Muscular dystrophies are a group of inherited disorders that cause degeneration of muscle, leading to weak and impaired movements. A central feature of all muscular dystrophies is that they are progressive in nature. Muscular dystrophies include, but are not limited to: Duchenne muscular dystrophy (DMD), Becker muscular dystrophy, Emery-Dreifuss muscular dystrophy, facioscapulohumeral muscular dystrophy, limb-girdle muscular dystrophies, and myotonic dystrophy Types 1 and 2, including the congenital form of Myotonic dystrophy Type 1. Symptoms may vary by type of muscular dystrophy with some or all muscles being affected. Exemplary symptoms of muscular dystrophies include delayed development of muscle motor skills, difficulty using one or more muscle groups, difficulty swallowing, speaking or eating, drooling, eyelid drooping, frequent falling, loss of strength in a muscle or group of muscles as an adult, loss in muscle size, problems walking due to weakness or altered biomechanics of the body, and/or cognitive or behavioral impairment/mental retardation.

While there are no known cures for muscular dystrophies, several supportive treatments are used which include both symptomatic and disease modifying therapies. Corticosteroids, ACE inhibitors, Angiotensin receptor blockers, physical therapy, orthotic devices, wheelchairs, or other assistive medical devices for ADLs and pulmonary function are commonly used in muscular dystrophies. Cardiac pacemakers are used to prevent sudden death from cardiac arrythmias in Myotonic dystrophy. Anti-myotonic agents which improve the symptoms of myotonia (inability to relax) include mexilitine, and in some cases phenytoin, procainamide and quinine.

Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a recessive X-linked form of muscular dystrophy which results in muscle degeneration and eventual death. DMD is characterized by weakness in the proximal muscles, abnormal gait, hypertrophy in the gastrocnemius (calf) muscles, and elevated creatine kinase. Many DMD patients are diagnosed around the age of 5, when symptoms/signs typically become more obvious. Affected individuals typically stop walking around age 10-13 and die in or before their mid to late 20's due to respiratory complications and cardiomyopathy.

In individuals affected with DMD, serum creatine kinase levels may be increased by greater than 10-fold as compared to unaffected individuals. In some embodiments, administering the provided composition to an affected individual results in a reduced serum creatine kinase level as compared to the baseline level before treatment. Typically, the baseline level is measured immediately before treatment. In some embodiments, administering the provided composition results in a reduced serum creatine kinase level by at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% as compared to the baseline serum creatine kinase level immediately before treatment. In some embodiments, administering the provided composition results in a reduced serum creatine kinase level to less than about 3500 IU/L, 3000 IU/L, 2500 IU/L, 2000 IU/L, 1500 IU/L, 1000 IU/L, 750 IU/L, 500 IU/L, 250 IU/L, 100 IU/L, 90 IU/L, 80 IU/L, 70 IU/L or 60 IU/L. In some embodiments, administering the provided composition results in a reduced serum creatine kinase level as compared to the serum creatine kinase level in subjects who are not treated.

The disorder DMD is caused by a mutation in the dystrophin gene, located on the human X chromosome, which codes for the protein dystrophin, an important structural component within muscle tissue that provides structural stability to the dystroglycan complex (DGC) of the cell membrane. Dystrophin links the internal cytoplasmic actin filament network and extracellular matrix, providing physical strength to muscle fibers. Accordingly, alteration or absence of dystrophin results in abnormal sarcolemma membrane tearing and necrosis of muscle fibers. While both sexes can carry the mutation, females rarely exhibit severe signs of the disease.

A main symptom of DMD is muscle weakness associated with muscle wasting with the voluntary muscles being first affected typically, especially affecting the muscles of the hips, pelvic area, thighs, shoulders, and calf muscles. Muscle weakness also occurs in the arms, neck, and other areas. Calves are often enlarged. Signs and symptoms usually appear before age 6 and may appear as early as infancy. Cardiomyopathy occurs in individuals with DMD usually after the age of 18. Other physical symptoms include, but are not limited to, delayed ability to walk independently, progressive difficulty in walking, stepping, or running, and eventual loss of ability to walk (usually by the age of 12); frequent falls; fatigue; difficulty with motor skills (running, hopping, jumping); increased lumbar lordosis, leading to shortening of the hip-flexor muscles; impaired functionality of achilles tendon and hamstrings, fibrosis in connective tissue; muscle fiber deformities; pseudohypertrophy (enlarging) of tongue and calf muscles caused by replacement of muscle tissue by fat and connective tissue; higher risk of neurobehavioral disorders (e.g., ADHD), learning disorders (dyslexia), and non-progressive weaknesses in specific cognitive skills (in particular short-term verbal memory); skeletal deformities (including scoliosis in some cases).

The changes in muscle seen in DMD are accompanied by an increase in connective tissue, i.e., the development of fibrosis, and result from either reactive or reparative processes involving mechanical, humoral and or cellular factors. Lack of functional dystrophin leads to instability of muscle fiber membranes, and as a result, the cells are less resistant to mechanical shear and prone to excess influx of electrolytes resulting in tissue damage. As muscle tissue in DMD is damaged, recovery is limited by the ability of satellite cells to proliferate. This leads to necrosis, inflammation, fibrosis and fatty cell replacement. The increase in connective tissue occurs early in the disease process as areolar connective tissue that ensheaths each myocyte and overlays the sarcolemma (i.e., the endomysium) increases prior to observable muscle damage. The increase in collagenous connective tissue is a factor in muscle pathology in DMD, adversely affecting the supply of nutrients to the affected myocyte, and secondarily affecting muscle strength and age of loss of ambulation.

In some embodiments, administration of an anti-Flt-1 antibody, or antigen-binding fragment thereof, in vivo results in decreased fibrosis of muscle tissue. In some embodiments the muscle is skeletal muscle. In particular embodiments, the muscle is the cardiac muscle, diaphragm muscle, gastrocnemius muscle and/or tibialis anterior (TA) muscle. In some embodiments, the decreased fibrosis is demonstrated by decreased collagen staining. In some embodiments, the collagen in Type I collagen. In some embodiments, the decreased fibrosis may be measured, for example, by measuring the percent collagen positive area in muscle of mice administered the anti-Flt-1 antibody, or antigen-binding fragment thereof. For example, the percent collagen positive area in the diaphragm muscle of mice administered the anti-Flt-1 antibody, or antigen-binding fragment thereof, may be at least about 3.0%, about 3.5%, about 4.0%, about 4.5%, about 5.0%, about 5.5%, about 6.0%, about 6.5%, about 7.0%, about 7.5%, about 8.0%, about 8.5% or about 9.0% of the total tissue area. In a particular embodiment, the percent collagen positive area in the diaphragm muscle of mice administered the anti-Flt-1 antibody may be significantly lower than the percent collagen positive area in the diaphragm muscle of mice administered an isotype control antibody.

In some embodiments, administration of an anti-Flt-1 antibody, or antigen-binding fragment thereof, in vivo results in decreased necrosis of muscle tissue. In some embodiments the muscle is skeletal muscle. In particular embodiments, the muscle is the cardiac muscle, diaphragm muscle, gastrocnemius muscle and/or tibialis anterior (TA) muscle. In some embodiments, the decreased necrosis may be measured, for example, by measuring the percent necrosis positive area in muscle of mice administered the anti-Flt-1 antibody, or antigen-binding fragment thereof. For example, the percent necrosis positive area in the gastrocnemius muscle of mice administered the anti-Flt-1 antibody, or antigen-binding fragment thereof may be at least about 0.5%, about 0.45%, about 0.4%, about 0.35%, about 0.3%, about 0.25%, about 0.2%, about 0.15%, about 0.1%, about 0.05%, or about 0.025% of the total tissue area. In a particular embodiment, the percent necrosis positive area in the gastrocnemius muscle of mice administered the anti-Flt-1 antibody may be significantly lower than the percent necrosis positive area in the gastrocnemius muscle of mice administered an isotype control antibody.

In some embodiments, administration of an anti-Flt-1 antibody, or antigen-binding fragment thereof, in vivo results in increased muscle force and/or resistance to fatigue.

Flt-1 Receptor

Flt-1 receptor, also known as vascular endothelial growth factor receptor 1 (VEGFR-1) or Flt-1, is a receptor that is encoded by the FLT1 gene and expressed on endothelia cell and monocyte cell membranes. The vascular endothelial growth factor (VEGF) family of signal glycoproteins act as potent promoters of angiogenesis during embryogenesis and postnatal growth. Specifically, the binding of the VEGF-A ligand with the VEGF receptors has been shown to promote vascular permeability and also trigger endothelial cell migration, proliferation, and survival, and the newly formed endothelial cells provide the basic structure of new vasculatures. The dominant VEGF signal molecule for angiogenesis, VEGF-A, mediates its signal through VEGF receptor-1 (VEGFR-1, also known as Flt-1) and VEGF receptor-2 (VEGFR-2, also known as Flk-1). A soluble form of Flt-1 (sFlt-1) also exists, but lacks an intracellular signaling domain and thus is believed to only serve in a regulatory capacity by sequestering VEGF-A or other ligands that bind to it. sFlt-1 and other molecules containing Flt-1 binding sites that are not linked to an intracellular signal transduction pathway are referred to as “decoy receptors”. Flt-1 and Flk-1 receptors contain an extracellular VEGF-A-binding domain and an intracellular tyrosine kinase domain, and both show expression during the developmental stage and tissue regeneration in hemangioblasts and endothelial cell lineages. Flt-1 has about 10 times greater binding affinity for VEGF-A (K_(a)˜2⁻¹⁰ pM) compared to Flk-1, but weaker tyrosine kinase activity indicates that angiogenic signal transduction following VEGF-A binding to Flt-1 is comparably weaker than that resulting from VEGF-A binding to Flk-1. As such, homozygous Flt-1 gene knockout mice die in the embryonic stage from endothelial cell overproduction and blood vessel disorganization. Inversely, homozygous Flk-1 gene knockout mice die from defects in the development of organized blood vessels due to lack of yolk-sac blood island formation during embryogenesis. Both the Flt-1 and Flk-1 receptors are needed for normal development, but selective augmentation in VEGF-A concentration may allow for greater binding to the Flk-1 receptor and induce a pro-angiogenic effect that increases capillary density and facilitates regeneration of muscle, reduction of fibrosis and inflammation, and mitigation of symptoms and features associated with DMD and other muscular dystrophies in various muscle tissues.

As used herein, the term “Flt-1 receptor” refers to both soluble and membrane associate Flt-1 receptors, or functional fragments thereof.

Anti-Flt-1 Antibodies

As used herein, the term “anti-Flt-1 antibodies” refers to any antibodies, or antigen-binding fragments thereof, that bind to a Flt-1 receptor (e.g., soluble or membrane associated Flt-1 receptor). In some embodiments, anti-Flt-1 antibodies are produced that bind with high affinity to Flt-1 receptors. Without wishing to be bound by theory, it is believed that anti-Flt-1 antibody binding to Flt-1 receptors inhibits one or more endogenous ligands from binding to Flt-1 and thereby allowing a greater amount of available ligand to associate with other VEGF receptors, such as the Flk-1 receptor. Increased availability of VEGF promotes angiogenesis with increased blood flow to muscle to combat functional ischemia and leading to improvements in structural and functional characteristics of DMD. In some embodiments, antibody binding to Flt-1 receptors increases the amount of VEGF available to bind to other VEGF receptors.

In some embodiments the anti-Flt-1 antibody or antigen-binding fragment thereof comprises the sequences provided in Table 2.

TABLE 2 Heavy Chain Variable Region CDR1 CDR2 CDR3 IGHV3-23*01 SYAMS AISGSGGSTYYADSVKG --------------DY (SEQ ID NO: 1) (SEQ ID NO: 5) (SEQ ID NO: 15) IGHV3-23*04 SYAMS AISGSGGSTYYADSVKG --------------DY (SEQ ID NO: 1) (SEQ ID NO: 5) (SEQ ID NO: 15) 13B4_VH DYSMS AISWNGDSTYYAESMKG SWATPIESLYYYGMDY (SEQ ID NO: 2) (SEQ ID NO: 6) (SEQ ID NO: 16) 27H4_VH(97.6_1.0 DYSMS AISWNGDSTYYAESLKG SWATPIESLYYYGSDY (SEQ ID NO: 2) (SEQ ID NO: 7) (SEQ ID NO: 17) 27H9_VH(97.5_1.1 DYSMS AISWNGDSTYYAESAKG SWATPIESLYYYGSDY (SEQ ID NO: 2) (SEQ ID NO: 8) (SEQ ID NO: 17) 25D4_VH(97.0_0.9 DYSAS AISWNGDSTYYAESVKG SWATPIESLYYYGSDY (SEQ ID NO: 3) (SEQ ID NO: 9) (SEQ ID NO: 17) 25G9_VH(97.0_0.9 DYSMS AITWSGDSTYYAESVKG SWATPIESLYYYGTDY SEQ ID NO: 2) (SEQ ID NO: 10) (SEQ ID NO: 18) 25F11_VH(97.5_1. DYSMS AISWNGDSTYYAESAKG SWATPIESLYYYGSDY (SEQ ID NO: 2) (SEQ ID NO: 8) (SEQ ID NO: 17) 29E2_VH(96.3_1.1 DYSLS AISWNGDSTYYAESVKG SWATPIESLYYYGSDY (SEQ ID NO: 4) (SEQ ID NO: 9) (SEQ ID NO: 17) 27G9_VH(96.3_1.3 DYSAS AISWSGDSTYYAESLKG SWATPIESLYYYGSDY (SEQ ID NO: 3) (SEQ ID NO: 11) (SEQ ID NO: 17) 27H6_VH(97.5 DYSAS AISWSGDSTYYAESVKG SWATPIESLYYYGSDY (SEQ ID NO: 3) (SEQ ID NO: 12) (SEQ ID NO: 17) 27H9_NG/QG DYSMS AISWQGDSTYYAESAKG SWATPIESLYYYGSDY (SEQ ID NO: 2) (SEQ ID NO: 13) (SEQ ID NO: 17) 27H9_NG/NA DYSMS AISWNADSTYYAESAKG SWATPIESLYYYGSDY (SEQ ID NO: 2) (SEQ ID NO: 14) (SEQ ID NO: 17) 27H9_NA_+_AAA DYSMS AISWNADSTYYAESAKG SWATPIESLYYYGSDY (SEQ ID NO: 2) (SEQ ID NO: 14) (SEQ ID NO: 17) Light Chain Variable Region CDR1 CDR2 CDR3 IGLV3-9*01 GGNNIGSKNVH RDSNRPS QV-------VV (SEQ ID NO: 19) (SEQ ID NO: 22) (SEQ ID NO: 25) IGLV3-9*02 GGNNLGYKSVH RDNNRPS QV-------VV (SEQ ID NO: 20) (SEQ ID NO: 23) (SEQ ID NO: 25) LC_21B3 GGNNIGSQTAQ ANNRRPS QVWDGSTQAIV (SEQ ID NO: 21) (SEQ ID NO: 24) (SEQ ID NO: 26) VL_27H4 GGNNIGSQTAQ ANNRRPS QVWEDSTQAIV (SEQ ID NO: 21) (SEQ ID NO: 24) (SEQ ID NO: 27) VL_27H9 GGNNIGSQTAQ ANNRRPS QVWDESTQAIV (SEQ ID NO: 21) (SEQ ID NO: 24) (SEQ ID NO: 28) VL_25D4 GGNNIGSQTAQ ANNRRPS QVWAASTQAIV (SEQ ID NO: 21) (SEQ ID NO: 24) (SEQ ID NO: 29) VL_25G9 GGNNIGSQTAQ ANNRRPS QVWDDSTQAIV (SEQ ID NO: 21) (SEQ ID NO: 24) (SEQ ID NO: 30) VL_25F11 GGNNIGSQTAQ ANNRRPS QVWEASTQAIV (SEQ ID NO: 21) (SEQ ID NO: 24) (SEQ ID NO: 31) VL_29E2 GGNNIGSQTAQ ANNRRPS QVWDASTQAIV (SEQ ID NO: 21) (SEQ ID NO: 24) (SEQ ID NO: 32) VL_27G9 GGNNIGSQTAQ ANNRRPS QVWEESTQAIV (SEQ ID NO: 21) (SEQ ID NO: 24) (SEQ ID NO: 33) VL_27H6 GGNNIGSQTAQ ANNRRPS QVWDGSTQAIV (SEQ ID NO: 21) (SEQ ID NO: 24) (SEQ ID NO: 26) VL_27H6(DA) GGNNIGSQTAQ ANNRRPS QVWDASTQAIV (SEQ ID NO: 21) (SEQ ID NO: 24) (SEQ ID NO: 32) VL_27H6(EG) GGNNIGSQTAQ ANNRRPS QVWEGSTQAIV (SEQ ID NO: 21) (SEQ ID NO: 24) (SEQ ID NO: 34) Heavy Chain Variable Region VH IGHV3-23*01 EVQLLESGGGLVQPGGSLRLSCAASGFTFS SYAMS WVRQAPGKGLEWVS AISGSGGSTYYADSVKG RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAK -------- ------DY WGQGTLVTVSS (SEQ ID NO: 35) IGHV3-23*04 EVQLVESGGGLVQPGGSLRLSCAASGFTFS SYAMS WVRQAPGKGLEWVS AISGSGGSTYYADSVKG RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAK -------- ------DY WGQGTLVTVSS (SEQ ID NO: 36) 13B4_VH ELQLVESGGGLVQPGGSLRLSCAASGFTFR DYSMS WVRQAPGKGLEWVS AISWNGDSTYYAESMKG RFTISRDNAKNTLYLQMNSLKSEDTAVYYCAK SWATPIESLYYYGMDY WGKGTLVTVSS (SEQ ID NO: 37) 27H4_VH(97.6_1.0 ELQLVESGGGLVQPGGSLRLSCAASGFTFR DYSMS WVRQAPGKGLEWVS AISWNGDSTYYAESLKG RFTISRDNAKNTLYLQMNSLRAEDTAVYYCAK SWATPIESLYYYGSDY WGQGTLVTVSS (SEQ ID NO: 38) 27H9_VH(97.5_1.1 EVQLLESGGGLVQPGGSLRLSCAASGFTFR DYSMS WVRQAPGKGLEWVS AISWNGDSTYYAESAKG RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAK SWATPIESLYYYGSDY WGQGTLVTVSS (SEQ ID NO: 39) 25D4_VH(97.0_0.9 EVQLLESGGGLVQPGGSLRLSCAASGFTFR DYSAS WVRQAPGKGLEWVS AISWNGDSTYYAESVKG RFTISRDNAKNTLYLQMNSLRAEDTAVYYCAK SWATPIESLYYYGSDY WGQGTLVTVSS (SEQ ID NO: 40) 25G9_VH(97.0_0.9 EVQLLESGGGLVQPGGSLRLSCAASGFTFR DYSMS WVRQAPGKGLEWVS AITWSGDSTYYAESVKG RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAK SWATPIESLYYYGTDY WGKGTLVTVSS (SEQ ID NO: 41) 25F11_VH(97.5_1. EVQLLESGGGLVQPGGSLRLSCAASGFTFR DYSMS WVRQAPGKGLEWVS AISWNGDSTYYAESAKG RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAK SWATPIESLYYYGSDY WGQGTLVTVSS (SEQ ID NO: 42) 29E2_VH(96.3_1.1 EVQLVESGGGLVQPGGSLRLSCAASGFTFR DYSLS WVRQAPGKGLEWVS AISWNGDSTYYAESVKG RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAK SWATPIESLYYYGSDY WGKGTLVTVSS (SEQ ID NO: 43) 27G9_VH(96.3_1.3 EVQLLESGGGLVQPGGSLRLSCAASGFTFR DYSAS WVRQAPGKGLEWVS AISWSGDSTYYAESLKG RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAK SWATPIESLYYYGSDY WGKGTLVTVSS (SEQ ID NO: 44) 27H6_VH(97.5 ELQLVESGGGLVQPGGSLRLSCAASGFTFS DYSAS WVRQAPGKGLEWVS AISWSGDSTYYAESVKG RFTIFRDNSKNTLYLQMNSLRAEDTAVYYCAK SWATPIESLYYYGSDY WGQGTLVTVSS (SEQ ID NO: 45) 27H9_NG/QG EVQLLESGGGLVQPGGSLRLSCAASGFTFR DYSMS WVRQAPGKGLEWVS AISWQGDSTYYAESAKG RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAK SWATPIESLYYYGSDY WGQGTLVTVSS (SEQ ID NO: 46) 27H9_NG/NA EVQLLESGGGLVQPGGSLRLSCAASGFTFR DYSMS WVRQAPGKGLEWVS AISWNADSTYYAESAKG RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAK SWATPIESLYYYGSDY WGQGTLVTVSS (SEQ ID NO: 47) 27H9_NA_+_AAA EVQLLESGGGLVQPGGSLRLSCAASGFTFR DYSMS WVRQAPGKGLEWVS AISWNADSTYYAESAKG RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAK SWATPIESLYYYGSDY WGQGTLVTVSS (SEQ ID NO: 48) Light Chain Variable Region VL IGLV3-9*01 SYELTQPLSVSVALGQTARITC GGNNIGSKNVH WYQQKPGQAPVLVIY RDSNRPS GIPERFSGSNSGNTATLTISRAQAGDEADYYC QV-------VV FGGGTKLTVL (SEQ ID NO: 49) IGLV3-9*02 SYELTQPLSVSVALGQAARITC GGNNLGYKSVH WYQQKPGQAPVLVIY RDNNRPS GIPERFSGSNSGNTATLTISRAQAGDEADYYC QV-------VV FGGGTKLTVL (SEQ ID NO: 50) LC_21B3 SYELTQSPSVSVALRQTAKITC GGNNIGSQTAQ WYQQKPGQAPVLVIY ANNRRPS GIPERFSGSKSGNTATLTISGAQAEDEADYYC QVWDGSTQAIV FGGGTHLTVL (SEQ ID NO: 51) VL_27H4 SYELTQPLSVSVALGQTARITC GGNNIGSQTAQ WYQQKPGQAPVLVIY ANNRRPS GIPERFSGSKSGNTATLTISRAQAEDEADYYC QVWEDSTQAIV FGGGTKLTVL (SEQ ID NO: 52) VL_27H9 SYELTQPLSVSVALRQTARITC GGNNIGSQTAQ WYQQKPGQAPVLVIY ANNRRPS GIPERFSGSKSGNTATLTISRAQAEDEADYYC QVWDESTQAIV FGGGTKLTVL (SEQ ID NO: 53) VL_25D4 SYELTQPLSVSVALGQTARITC GGNNIGSQTAQ WYQQKPGQAPVLVIY ANNRRPS GIPERFSGSKSGNTATLTISGAQAEDEADYYC QVWAASTQAIV FGGGTKLTVL (SEQ ID NO: 54) VL_25G9 SYELTQPLSVSVALRQAARITC GGNNIGSQTAQ WYQQKPGQAPVLVIY ANNRRPS GIPERFSGSKSGNTATLTISRAQAEDEADYYC QVWDDSTQAIV FGGGTKLTVL (SEQ ID NO: 55) VL_25F11 SYELTQPLSVSVALRQAARITC GGNNIGSQTAQ WYQQKPGQAPVLVIY ANNRRPS GIPERFSGSKSGNTATLTISRAQAEDEADYYC QVWEASTQAIV FGGGTKLTVL (SEQ ID NO: 56) VL_29E2 SYELTQSPSVSVALRQTAKITC GGNNIGSQTAQ WYQQKPGQAPVLVIY ANNRRPS GIPERFSGSKSGNTATLTISGAQAGDEADYYC QVWDASTQAIV FGGGTKLTVL (SEQ ID NO: 57) VL_27G9 SYELTQPLSVSVALGQTAKITC GGNNIGSQTAQ WYQQKPGQAPVLVIY ANNRRPS GIPERFSGSKSGNTATLTISRAQAEDEADYYC QVWEESTQAIV FGGGTHLTVL (SEQ ID NO: 58) VL_27H6 SYELTQPLSVSVALRQAAKITC GGNNIGSQTAQ WYQQKPGQAPVLVIY ANNRRPS GIPERFSGSKSGNTATLTISRAQAGDEADYYC QVWDGSTQAIV FGGGTKLTVL (SEQ ID NO: 59) VL_27H6(DA) SYELTQPLSVSVALRQAAKITC GGNNIGSQTAQ WYQQKPGQAPVLVIY ANNRRPS GIPERFSGSKSGNTATLTISRAQAGDEADYYC QVWDASTQAIV FGGGTKLTVL (SEQ ID NO: 60) VL_27H6(EG) SYELTQPLSVSVALRQAAKITC GGNNIGSQTAQ WYQQKPGQAPVLVIY ANNRRPS GIPERFSGSKSGNTATLTISRAQAGDEADYYC QVWEGSTQAIV FGGGTKLTVL (SEQ ID NO: 61) Heavy Chain Heavy Chain Sequence (VH + CH1/2/3) VH_27H6_DG/EG ELQLVESGGGLVQPGGSLRLSCAASGFTFSDYSASWVRQAPGKGLEWVSAISWSGDSTY YAESVKGRFTIFRDNSKNTLYLQMNSLRAEDTAVYYCAKSWATPIESLYYYGSDYWGQG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 62) VH_27H6_DG/DA ELQLVESGGGLVQPGGSLRLSCAASGFTFSDYSASWVRQAPGKGLEWVSAISWSGDSTY YAESVKGRFTIFRDNSKNTLYLQMNSLRAEDTAVYYCAKSWATPIESLYYYGSDYWGQG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 63) VH_27H9_NG/QG EVQLLESGGGLVQPGGSLRLSCAASGFTFRDYSMSWVRQAPGKGLEWVSAISWQGDSTY YAESAKGRFTISRDNSKNTLYLQMNSLRAEDTAVYYCAKSWATPIESLYYYGSDYWGQG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 64) VH_27H9_NG/NA EVQLLESGGGLVQPGGSLRLSCAASGFTFRDYSMSWVRQAPGKGLEWVSAISWNADSTY YAESAKGRFTISRDNSKNTLYLQMNSLRAEDTAVYYCAKSWATPIESLYYYGSDYWGQG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 65) VH_27H4_NG/QG ELQLVESGGGLVQPGGSLRLSCAASGFTFRDYSMSWVRQAPGKGLEWVSAISWQGDSTY YAESLKGRFTISRDNAKNTLYLQMNSLRAEDTAVYYCAKSWATPIESLYYYGSDYWGQG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 66) VH_27H4_NG/NA ELQLVESGGGLVQPGGSLRLSCAASGFTFRDYSMSWVRQAPGKGLEWVSAISWNADSTY YAESLKGRFTISRDNAKNTLYLQMNSLRAEDTAVYYCAKSWATPIESLYYYGSDYWGQG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 67) VH_27H4_NA_+_AAA ELQLVESGGGLVQPGGSLRLSCAASGFTFRDYSMSWVRQAPGKGLEWVSAISWNADSTY YAESLKGRFTISRDNAKNTLYLQMNSLRAEDTAVYYCAKSWATPIESLYYYGSDYWGQG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPEAAGAPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 68) VH_27H9_NA_+_AAA EVQLLESGGGLVQPGGSLRLSCAASGFTFRDYSMSWVRQAPGKGLEWVSAISWNADSTY YAESAKGRFTISRDNSKNTLYLQMNSLRAEDTAVYYCAKSWATPIESLYYYGSDYWGQG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPEAAGAPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 69) VH_21B3_AAA ELQLVESGGGLVQPGGSLRLSCAASGFTFRDYSMSWVRQAPGKGLEWVSAISWNGDSTY YAESMKGRFTISRDNAKNTLYLQMNSLKSEDTAVYYCAKSWATPIESLYYYGMDYWGKG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPEAAGAPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 70) VH_27H6 ELQLVESGGGLVQPGGSLRLSCAASGFTFSDYSASWVRQAPGKGLEWVSAISWSGDSTY YAESVKGRFTIFRDNSKNTLYLQMNSLRAEDTAVYYCAKSWATPIESLYYYGSDYWGQG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 71) VH_27H4 ELQLVESGGGLVQPGGSLRLSCAASGFTFRDYSMSWVRQAPGKGLEWVSAISWNGDSTY YAESLKGRFTISRDNAKNTLYLQMNSLRAEDTAVYYCAKSWATPIESLYYYGSDYWGQG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 72) VH_27H9 EVQLLESGGGLVQPGGSLRLSCAASGFTFRDYSMSWVRQAPGKGLEWVSAISWNGDSTY YAESAKGRFTISRDNSKNTLYLQMNSLRAEDTAVYYCAKSWATPIESLYYYGSDYWGQG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 73) HC_13B4 ELQLVESGGGLVQPGGSLRLSCAASGFTFRDYSMSWVRQAPGKGLEWVSAISWNGDSTY YAESMKGRFTISRDNAKNTLYLQMNSLKSEDTAVYYCAKSWATPIESLYYYGMDYWGKG TLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKSYFPEPVTVSWNSGALTSGVHT FPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPP CPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFF LYSKLTVDKSRWQQGNVFSCSVMNEALHNHYTQKSLSLSPGK (SEQ ID NO: 74) Light Chain Light Chain Sequence (VL + CL) LC_27H6_DG/EG SYELTQPLSVSVALRQAAKITCGGNNIGSQTAQWYQQKPGQAPVLVIYANNRRPSGIPE RFSGSKSGNTAILTISRAQAGDEADYYCQVWEGSTQAIVEGGGIKLIVLGQPKAAPSVT LFPPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAAS SYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS (SEQ ID NO: 75) LC_27H6_DG/DA SYELTQPLSVSVALRQAAKITCGGNNIGSQTAQWYQQKPGQAPVLVIYANNRRPSGIPE RFSGSKSGNTAILTISRAQAGDEADYYCQVWDASTQAIVEGGGIKLIVLGQPKAAPSVT LFPPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAAS SYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS (SEQ ID NO: 76) LC_27H9_NG/QG SYELTQPLSVSVALRQTARITCGGNNIGSQTAQWYQQKPGQAPVLVIYANNRRPSGIPE RFSGSKSGNTAILTISRAQAEDEADYYCQVWDESTQAIVEGGGIKLIVLGQPKAAPSVT LFPPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAAS SYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS (SEQ ID NO: 77) LC_27H9_NG/NA SYELTQPLSVSVALRQTARITCGGNNIGSQTAQWYQQKPGQAPVLVIYANNRRPSGIPE RFSGSKSGNTAILTISRAQAEDEADYYCQVWDESTQAIVEGGGIKLIVLGQPKAAPSVT LFPPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAAS SYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS (SEQ ID NO: 78) LC_27H4_NG/QG SYELTQPLSVSVALGQTARITCGGNNIGSQTAQWYQQKPGQAPVLVIYANNRRPSGIPE RFSGSKSGNTAILTISRAQAEDEADYYCQVWEDSTQAIVEGGGIKLIVLGQPKAAPSVT LFPPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAAS SYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS (SEQ ID NO: 79) LC_27H4_NG/NA SYELTQPLSVSVALGQTARITCGGNNIGSQTAQWYQQKPGQAPVLVIYANNRRPSGIPE RFSGSKSGNTATLTISRAQAEDEADYYCQVWEDSTQAIVEGGGTKLTVLGQPKAAPSVT LFPPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAAS SYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS (SEQ ID NO: 80) LC_27H4_NA_+_AAA SYELTQPLSVSVALGQTARITCGGNNIGSQTAQWYQQKPGQAPVLVIYANNRRPSGIPE RFSGSKSGNTATLTISRAQAEDEADYYCQVWEDSTQAIVEGGGTKLTVLGQPKAAPSVT LFPPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAAS SYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS (SEQ ID NO: 81) LC_27H9_NA_+_AAA SYELTQPLSVSVALRQTARITCGGNNIGSQTAQWYQQKPGQAPVLVIYANNRRPSGIPE RFSGSKSGNTATLTISRAQAEDEADYYCQVWDESTQAIVEGGGTKLTVLGQPKAAPSVT LFPPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAAS SYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS (SEQ ID NO: 82) LC_21B3_AAA SYELTQSPSVSVALRQTAKITCGGNNIGSQTAQWYQQKPGQAPVLVIYANNRRPSGIPE RFSGSKSGNTATLTISGAQAEDEADYYCQVWDGSTQAIVEGGGTHLTVLGQPKAAPSVT LFPPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAAS SYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS (SEQ ID NO: 83) LC_27H6 SYELTQPLSVSVALRQAAKITCGGNNIGSQTAQWYQQKPGQAPVLVIYANNRRPSGIPE RFSGSKSGNTATLTISRAQAGDEADYYCQVWDGSTQAIVEGGGTKLTVLGQPKAAPSVT LFPPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAAS SYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS (SEQ ID NO: 84) LC_27H4 SYELTQPLSVSVALGQTARITCGGNNIGSQTAQWYQQKPGQAPVLVIYANNRRPSGIPE RFSGSKSGNTATLTISRAQAEDEADYYCQVWEDSTQAIVEGGGTKLTVLGQPKAAPSVT LFPPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAAS SYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS (SEQ ID NO: 85) LC_27H9 SYELTQPLSVSVALRQTARITCGGNNIGSQTAQWYQQKPGQAPVLVIYANNRRPSGIPE RFSGSKSGNTATLTISRAQAEDEADYYCQVWDESTQAIVEGGGTKLTVLGQPKAAPSVT LFPPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAAS SYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS (SEQ ID NO: 86) Constant Region CH1-CH2-CH3 27H6_DG/EG ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELL GGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 87) 27H6_DG/DA ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELL GGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 87) 27H9_NG/QG ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELL GGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 87) 27H9_NG/NA ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELL GGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 87) 27H4_NG/QG ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELL GGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 87) 27H4_NG/NA ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELL GGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 87) 27H4_NA_+_AAA ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPEAA GAPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 88) 27H9_NA_+_AAA ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPEAA GAPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 88) 21B3_AAA ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPEAA GAPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 88) 27H6 ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELL GGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 87) 27H4 ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELL GGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 87) 27H9 ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELL GGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 87) 13B4 ASTKGPSVFPLAPSSKSTSGGTAALGCLVKSYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELL GGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREE QYNSTYRVVSVLIVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPP SRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTV DKSRWQQGNVFSCSVMNEALHNHYTQKSLSLSPGK (SEQ ID NO: 89)

In some embodiments, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises one or more complementarity determining regions (CDR) selected from the group consisting of a VL CDR1 defined by an amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:19 to SEQ ID NO:21, a VL CDR2 defined by an amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:22 to SEQ ID NO:24, a VL CDR3 defined by an amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:25 to SEQ ID NO:34, a VH chain CDR1 defined by an amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:1 to SEQ ID NO:4, a VH CDR2 defined by an amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:5 to SEQ ID NO:14, and a VH CDR3 defined by an amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:15 to SEQ ID NO:18. In some embodiments, the VL CDR3 is not SEQ ID NO:25. In some embodiments, the VH CDR3 is not SEQ ID NO:15.

In some embodiments, the one or more CDRs comprise the VL CDR3 defined by the amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:25 to SEQ ID NO:34; and the VH CDR3 defined by the amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:15 to SEQ ID NO:18. In some embodiments, the VL CDR3 is not SEQ ID NO:25. In some embodiments, the VH CDR3 is not SEQ ID NO:15.

In some embodiments, the one or more CDRs comprise the VL CDR1 defined by the amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:19 to SEQ ID NO:21, the VL CDR2 defined by the amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:22 to SEQ ID NO:24, and the VL CDR3 defined by amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:25 to SEQ ID NO:34. In some embodiments, the VL CDR3 is not SEQ ID NO:25.

In some embodiments, the one or more CDRs comprise the VH CDR1 defined by the amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:1 to SEQ ID NO:4, the VH CDR2 defined by the amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:5 to SEQ ID NO:14, and the VH CDR3 defined by the amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:15 to SEQ ID NO:18. In some embodiments, the VH CDR3 is not SEQ ID NO:15.

In some embodiments, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a VL chain comprising the VL CDR1, VL CDR2, and VL CDR3 defined by the amino acid sequence of SEQ ID NO:19, SEQ ID NO:22, and SEQ ID NO:25, respectively. In another embodiment, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a VL chain comprising the VL CDR1, VL CDR2, and VL CDR3 defined by the amino acid sequence of SEQ ID NO:20, SEQ ID NO:23, and SEQ ID NO:25, respectively. In yet another embodiment the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a VL chain comprising the VL CDR1 and VL CDR2 defined by the amino acid sequence of SEQ ID NO:21, SEQ ID NO:24, respectively, and the VL CDR3 defined by the amino acid sequence of SEQ ID NO:26, SEQ ID NO:27, SEQ ID NO:28, SEQ ID NO:29, SEQ ID NO:30, SEQ ID NO:31, SEQ ID NO:32, SEQ ID NO:33 or SEQ ID NO:34. In a particular embodiment, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a VL chain comprising the VL CDR1 defined by the amino acid sequence of SEQ ID NO:21, the VL CDR2 defined by the amino acid sequence of SEQ ID NO:24, and the VL CDR3 defined by the amino acid sequence of SEQ ID NO:32. In some embodiments, the VL CDR3 is not SEQ ID NO:25.

In another embodiment, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a VH chain comprising the VH CDR1, VH CDR2, and VH CDR3 defined by the amino acid sequences of SEQ ID NO:1, SEQ ID NO:5, and SEQ ID NO:15, respectively. In another embodiment, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a VH chain comprising a VH CDR1, VH CDR2, and VH CDR3 defined by the amino acid sequences of SEQ ID NO:2, SEQ ID NO:6, and SEQ ID NO:16, respectively. In another embodiment, the anti-Flt-1 antibody or antigen-binding fragment thereof, comprises a VH chain comprising a VH CDR1, VH CDR2, and VH CDR3 defined by the amino acid sequences of SEQ ID NO:2, SEQ ID NO:10, and SEQ ID NO:18, respectively. In another embodiment, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a VH chain comprising the VH CDR1 and the VH CDR3 defined by the amino acid sequences of SEQ ID NO:2 and SEQ ID NO:17, respectively, and the VH CDR2 defined by the amino acid sequence of SEQ ID NO:7, SEQ ID NO:8, SEQ ID NO:13 or SEQ ID NO:14. In another embodiment, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a VH chain comprising the VH CDR1 and the VH CDR3 defined by the amino acid sequences of SEQ ID NO:3 and SEQ ID NO:17, respectively, and a VH CDR2 defined by the amino acid sequence of SEQ ID NO:9, SEQ ID NO:11 or SEQ ID NO:12. In another embodiment, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a VH chain comprising the VH CDR1, VH CDR2, and VH CDR3 defined by the amino acid sequences of SEQ ID NO:4, SEQ ID NO:9, and SEQ ID NO:17, respectively. In a particular embodiment, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a VH chain comprising the VH CDR1 defined by the amino acid sequence of SEQ ID NO:3, the VH CDR2 defined by the amino acid sequence of SEQ ID NO:12 and the VH CDR3 defined by the amino acid sequence of SEQ ID NO:17. In some embodiments, the VH CDR3 is not SEQ ID NO:15.

In another embodiment, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a light chain VL region comprising an amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:49 to SEQ ID NO:61, and/or a heavy chain VH region comprising an amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:35 to SEQ ID NO:48. In a particular embodiment, the VL region comprises the amino acid sequence of SEQ ID NO:60 and the VH region comprises the amino acid sequence of SEQ ID NO:45. In another embodiment, the antibody further comprises a heavy chain constant region comprising an amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:87 to SEQ ID NO:89. In some embodiments, the VL region is not SEQ ID NO:49 or SEQ ID NO:50. In some embodiment, the VH region is not SEQ ID NO:35 or SEQ ID NO:36.

In another embodiment, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a light chain comprising an amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:75 to SEQ ID NO:86, and/or a heavy chain comprising an amino acid sequence having at least 60%, 70%, 80%, 90%, 95% or 98% identity to any one of SEQ ID NO:62 to SEQ ID NO:74. In a particular embodiment, the light chain comprises the amino acid sequence of SEQ ID NO:76 and the heavy chain region comprises the amino acid sequence of SEQ ID NO:71.

In some embodiments, the heavy chain of the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises the amino acid sequence MGWSCIILFLVATATGVHSELQLVESGGGLVQPGGSLRLSCAASGFTFSDYSASWVRQA PGKGLEWVSAISWSGDSTYYAESVKGRFTIFRDNSKNTLYLQMNSLRAEDTAVYYCAK SWATPIESLYYYGSDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDY FPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNT KVDKKVEPKSCDKTHTCPPCPAPEAAGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHE DPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSN KALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNG QPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSL SPGKX (SEQ ID NO:108). In some embodiments, the heavy chain of the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises the amino acid sequence

(SEQ ID NO: 109) ELQLVESGGGLVQPGGSLRLSCAASGFTFSDYSASWVRQAPGKGLEWVSA ISWSGDSTYYAESVKGRFTIFRDNSKNTLYLQMNSLRAEDTAVYYCAKSW ATPIESLYYYGSDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAAL GCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSS LGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPEAAGGPSVFL EPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPR EEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQ PREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYK TTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLS LSPGK.

In some embodiments, the light chain of the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises the amino acid sequence

(SEQ ID NO: 110) MGWSCIILFLVATATGVHSSYELTQPLSVSVALRQAAKITCGGNNIGSQT AQWYQQKPGQAPVLVIYANNRRPSGIPERFSGSKSGNTATLTISRAQAGD EADYYCQVWDASTQAIVFGGGTKLTVLGQPKAAPSVTLFPPSSEELQANK ATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAASSYLS LTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECSX.

In some embodiments, the anti-Flt-1 antibody, or antigen-binding fragment thereof, comprises a heavy chain of SEQ ID NO:108 or SEQ ID NO:109 and a light chain of SEQ ID NO:110 or SEQ ID NO:76.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof, binds human Flt-1 with an affinity greater than about 10⁻⁷M, greater than about 0.5×10⁻⁷, greater than about 10⁻⁸, greater than about 0.5×10⁻⁸, greater than about 10⁻⁹M, greater than about 0.5×10⁻⁹, greater than about 10⁻¹⁰ M, greater than about 0.5×10⁻¹⁰ M, greater than about 10⁻¹¹M, greater than about 0.5×10⁻¹¹M, greater than about 10⁻¹²M, or greater than about 0.5×10⁻¹²M. In other embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof, binds to mouse Flt-1 with an affinity greater than about 10⁻⁷M, greater than about 0.5×10⁻⁷, greater than about 10⁻⁸, greater than about 0.5×10⁻⁸, greater than about 10⁻⁹M, greater than about 0.5×10⁻⁹, greater than about 10⁻¹⁰ M, greater than about 0.5×10⁻¹⁰ M, greater than about 10⁻¹¹M, greater than about 0.5×10⁻¹¹M, greater than about 10⁻¹²M, or greater than about 0.5×10⁻¹²M. The affinity of an Flt-1 antibody may be measured, for example, in a surface plasmon resonance assay, such as a BIACORE assay.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof, is characterized by an IC₅₀ below about 500 pM, below about 400 pM, below about 300 pM, below about 200 pM, below about 100 pM, below about 50 pM, below about 25 pM, below about 10 pM, below about 5 pM or below about 1 pM in a competition assay with human Flt-1. In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof, is characterized by an IC₅₀ below about 500 pM, below about 400 pM, below about 300 pM, below about 200 pM, below about 100 pM, below about 50 pM, below about 25 pM, below about 10 pM, below about 5 pM or below about 1 pM in a competition assay with mouse Flt-1.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof inhibits the binding and/or activity of VEGF at the Flt-1 receptor. In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof, is characterized by an IC₅₀ below about 500 pM, below about 400 pM, below about 300 pM, below about 200 pM, below about 100 pM, below about 50 pM, below about 25 pM, below about 10 pM, below about 5 pM or below about 1 pM for inhibition of binding of VEGF to human Flt-1 in a competition assay.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof completes with, and or inhibits VEGF binding to soluble Flt-1. In other embodiments, the competition, and or inhibition, is in a dose dependent manner. In particular embodiments, the inhibition of binding of VEGF to Flt-1 results in increased phosphorylation of VEGF R2. Without intending to be bound by theory, binding of the anti-Flt-1 antibody, or antigen-binding fragment thereof to Flt-1 inhibits the binding of VEGF to Flt-1. Unbound VEGF binds VEGF R2 which may be demonstrated by measuring phosphorylation of VEGF R2. In particular embodiments, the anti-Flt-1 antibody, or antigen-binding fragment rescues VEGF R2 phosphorylation in a dose dependent manner. For example, VEGF R2 phosphorylation may be rescued by at least about 100%, about 95%, about 90%, about 85%, about 80%, about 75%, about 70%, about 65%, about 60%, about 55%, about 50%, about 45%, about 40%, about 35% about 30%, about 25%, about 20%, about 15%, about 10% or about 5%.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof provide greater than about 95%, greater than about 90%, greater than about 85%, greater than about 80%, greater than about 75%, greater than about 70%, greater than about 65%, greater than about 60%, greater than about 55%, greater than about 50%, greater than about 45%, greater than about 40%, greater than about 35%, greater than about 30%, greater than about 25%, greater than about 20%, greater than about 15%, or greater than about 10% rescue in a bioassay. In a particular embodiment the bioassay comprises human primary vein endothelial cells (HUVECs) stimulated with VEGF in the presence of sFlt-1 and an anti-Flt-1 antibody or antigen-binding fragment thereof. VEGF induced activation of cells may be assayed by determining the phosphorylation status of the VEGF R2 receptor. Data may be expressed as a percent rescue of the phosphorylation of the VEGF R2 receptor relative to the phosphorylation of the VEGF R2 receptor in the presence of sFlt-1 alone (e.g., without anti-Flt-1 antibodies).

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof, has a half-life of greater than about 200 hours, greater than about 150 hours, greater than about 100 hours, greater than about 95 hours, greater than about 90 hours, greater than about 85 hours, greater than about 80 hours, greater than about 75 hours, greater than about 70 hours, greater than about 65 hours, greater than about 60 hours, greater than about 55 hours, greater than about 50 hours or greater than about 45 hours, and ranges therein. In some embodiments, the half-life is measured in a mouse.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof, has a maximum serum concentration of greater than about 400 ug/mL, greater than 375 ug/mL, greater than about 350 ug/mL, greater than about 325 ug/mL, greater than about 300 ug/mL, greater than about 275 ug/mL, greater than about 250 ug/mL, greater than about 225 ug/mL, greater than about 200 ug/mL, greater than about 175 ug/mL, greater than about 150 ug/mL, greater than about 125 ug/mL, greater than about 100 ug/mL, greater than about 75 ug/mL or greater than about 50 ug/mL, and ranges therein. In some embodiments, the maximum serum concentration is measured in a mouse.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof selectively binds Flt-1 and has minimal or no appreciable binding to other VEGF receptors. In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof selectively binds Flt-1 and has minimal or no appreciable binding to VEGF R2 (Flk-1) and/or VEGF R3 (Flt-4).

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof has a ka of greater than about 1×10⁻³ M⁻¹ sec⁻¹, greater than about 1×10⁻⁴ M⁻¹ sec⁻¹, greater than about 1×10⁻⁵M⁻¹ sec⁻¹, greater than about 1×10⁻⁶ M⁻¹ sec⁻¹, or greater than about 1×10⁻⁷ M⁻¹ sec⁻¹ when binding to human Flt-1.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof has a kd of greater than about 1×10⁻³ sec⁻¹, greater than about 1×10⁻⁴ sec⁻¹, greater than about 1×10⁻⁵ sec⁻¹ or greater than about 1×10⁻⁶ sec⁻¹ when binding to human Flt-1.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof has a K_(D) of greater than about 1×10⁻⁸M, greater than about 1×10⁻⁹M, greater than about 1×10⁻¹⁰ M, greater than about 1×10⁻¹¹ M or greater than about 1×10⁻¹²M when binding to human Flt-1.

In some embodiments an anti-Flt-1 antibody, or antigen-binding fragment thereof binds to soluble Flt-1. In particular embodiments, the binding is dose-dependent wherein higher concentrations of antibody, or antigen-binding fragment thereof, bind greater amounts of soluble Flt-1.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof has a percent human identify of greater than about 99%, greater than about 98%, greater than about 97%, greater than about 96%, greater than about 95%, greater than about 94%, greater than about 93%, greater than about 92%, greater than about 91%, greater than about 90% or greater than about 80%.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof has a percent human homology of greater than about 99%, greater than about 98%, greater than about 97%, greater than about 96%, greater than about 95%, greater than about 94%, greater than about 93%, greater than about 92%, greater than about 91%, greater than about 90% or greater than about 80%.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof binds to Flt-1 protein. In some embodiment the Flt-1 protein is a recombinant protein, for example recombinant sFlt-1. In a particular embodiment, the anti-Flt-1 antibody, or antigen-binding fragment thereof binds human Flt-1 isoform 1 (NP_002010.2 GI:156104876; SEQ ID NO:90) (Table 13). In another embodiment the anti-Flt-1 antibody, or antigen-binding fragment thereof binds to human Flt-1 isoform X1 (XP_011533316.1 GI:767977511; SEQ ID NO:91). In another embodiment the anti-Flt-1 antibody, or antigen-binding fragment thereof binds to human Flt-1 isoform 2 precursor (NP_001153392.1 GI:229892220; SEQ ID NO:92). In yet another embodiment the anti-Flt-1 antibody, or antigen-binding fragment thereof binds to human Flt-1 isoform 3 precursor (NP_001153502.1 GI:229892300; SEQ ID NO:93). In another embodiment the anti-Flt-1 antibody, or antigen-binding fragment thereof binds to human Flt-1 isoform 4 precursor (NP_001153503.1 GI:229892302; SEQ ID NO:94).

In some embodiments the anti-Flt-1 antibody, or antigen-binding fragment thereof binds to a particular a epitope of the Flt-1 protein. For example, the anti-Flt-1 antibody or antigen-binding portion thereof binds to amino acids sequences as provided in Table 3.

TABLE 3 amino acid position based on SEQ ID NO: 90 Amino acid sequence SEQ ID NO 141-153 EIPEIIHMTEGRE SEQ ID NO: 95 193-206 IISNATYKEIGLLT SEQ ID NO: 96 130-138 DTGRPFVEM SEQ ID NO: 97 141-148 EIPEIIHM SEQ ID NO: 98 139-148 YSEIPEIIHM SEQ ID NO: 99 139-153 YSEIPEIIHMTEGRE SEQ ID NO: 100 178-206 IPDGKRIIWDSRKGFIISN SEQ ID NO: 101 ATYKEIGLLT 199-204 YKEIGL SEQ ID NO: 102 128-138 ISDTGRPFVEM SEQ ID NO: 103

In some embodiments, administration of an anti-Flt-1 antibody, or antigen-binding fragment thereof in vivo results in peak serum antibody levels of at least about 700 ug/mL, at least about 650 ug/mL, at least about 600 ug/mL, at least about 550 ug/mL, at least about 500 ug/mL, at least about 450 ug/mL, at least about 400 ug/mL, at least about 350 ug/mL, at least about 300 ug/mL, at least about 250 ug/mL, at least about 200 ug/mL, at least about 150 ug/mL, at least about 100 ug/mL, at least about 50 ug/mL, at least about 40 ug/mL, at least about 30 ug/mL, at least about 20 ug/mL, at least about 10 ug/mL or at least about 5 ug/mL, and ranges therein. In some embodiments, the peak serum antibody level is dose dependent.

In some embodiments, administration of an anti-Flt-1 antibody, or antigen-binding fragment thereof in vivo results in trough serum antibody levels of at least about 450 ug/mL, at least about 400 ug/mL, at least about 350 ug/mL, at least about 300 ug/mL, at least about 250 ug/mL, at least about 200 ug/mL, at least about 150 ug/mL, at least about 100 ug/mL, at least about 50 ug/mL or at least about 25 ug/mL, and ranges therein. In some embodiments, the trough serum antibody level is dose dependent.

In some embodiments, administration of an anti-Flt-1 antibody, or antigen-binding fragment thereof in vivo results in a decreased serum level of soluble Flt-1 as compared to a baseline level or as compared to a level in subjects administered vehicle alone. Typically, the baseline level is measured immediately before administration. In some embodiments, administration of the anti-Flt-1 antibody or antigen-binding fragment thereof results in a decreased serum level of soluble Flt-1 by at least about 95%, about 90%, about 80%, about 70%, about 60%, about 50%, about 40%, about 30%, about 20% or about 10% as compared to the baseline serum level of soluble Flt-1 immediately before administration. In some embodiments, administration of the anti-Flt-1 antibody, or antigen-binding fragment thereof results in a decreased serum level of soluble Flt-1 to less than about 4000 pg/mL, about 3500 pg/mL, about 3000 pg/mL, about 2500 pg/mL, about 2000 pg/mL, about 1750 pg/mL, about 1500 pg/mL, about 1250 pg/mL, about 1000 pg/mL, about 900 pg/mL, about 800 pg/mL, about 700 pg/mL, about 600 pg/mL, about 500 pg/mL, about 450 pg/mL, about 400 pg/mL, about 350 pg/mL, about 300 pg/mL, about 250 pg/mL, about 200 pg/mL, about 150 pg/mL, about, 100 pg/mL, about 50 pg/mL or about 10 pg/mL, and ranges therein. In some embodiments, administration of the anti-Flt-1 antibody, or antigen-binding fragment thereof results in a decreased serum level of soluble Flt-1 as compared to the serum level of soluble Flt-1 in a subject who is not administered the antibody or antigen-binding fragment thereof. In some embodiments, the decreased serum level of soluble Flt-1 is dose dependent.

In some embodiments, administration of an anti-Flt-1 antibody, or antigen-binding fragment thereof in vivo results in an increased serum level of VEGF as compared to a baseline level or as compared to a level in subjects treated with vehicle alone. Typically, the baseline level is measured immediately before treatment. In some embodiments, administration of the anti-Flt-1 antibody or antigen-binding fragment thereof results in an increased serum level of VEGF by at least about 95%, about 90%, about 80%, about 70%, about 60%, about 50%, about 40%, about 30%, about 20% or about 10% as compared to the baseline serum level of VEGF immediately before administration. In some embodiments, administration of the anti-Flt-1 antibody, or antigen-binding fragment thereof results in an increased serum level of VEGF to more than about 500 pg/mL, about 450 pg/mL, about 400 pg/mL, about 350 pg/mL, about 300 pg/mL, about 250 pg/mL, about 200 pg/mL, about 150 pg/mL, about 100 pg/mL about 50 pg/mL or about 25 pg/mL and ranges therein. In some embodiments, administration of the anti-Flt-1 antibody, or antigen-binding fragment thereof results in an increased serum level of VEGF as compared to the serum level of VEGF in a subject who is not treated. In some embodiments, the increased serum level of VEGF is dose dependent.

In some embodiments, administration of an anti-Flt-1 antibody, or antigen-binding fragment thereof in vivo results in increased angiogenesis in muscle tissue. In some embodiments the muscle is skeletal muscle. In particular embodiments, the muscle is the diaphragm muscle, the gastrocnemius muscle and/or the tibialis anterior (TA) muscle. In some embodiments, the increased angiogenesis is demonstrated by increased CD31 staining of an endothelial cell marker, for example, CD31. In some embodiments, the increased staining may be measured, for example, by measuring the percent CD31 positive area in muscle of mice administered the anti-Flt-1 antibody, or antigen-binding fragment thereof. For example, the percent CD31 positive area in the diaphragm muscle of mice administered the anti-Flt-1 antibody, or antigen-binding fragment thereof may be at least about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1.0%, about 1.1%, about 1.2%, about 1.3%, about 1.4%, about 1.5%, about 1.6%, about 1.7%, about 1.8%, about 1.9%, about 2.0%, about 2.1%, about 2.2%, about 2.3%, about 2.4% or about 2.5% of the total tissue area. In a further example, the percent CD31 positive area in the TA muscle of mice administered the anti-Flt-1 antibody, or antigen-binding fragment thereof may be at least about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9% or about 1.0% pf the total tissue area. In a particular embodiment, the percent CD31 positive area in the diaphragm muscle or TA muscle of mice administered the anti-Flt-1 antibody may be significantly higher than the percent CD31 positive area in the diaphragm muscle or TA muscle of mice administered an isotype control antibody.

In some embodiments, the increased staining of an endothelial cell marker may be measured, for example, by measuring the normalized CD31 percent positivity in the muscle of mice administered the anti-Flt-1 antibody, or antigen-binding fragment thereof. In particular embodiments the increased CD31 staining the muscle of mice administered the anti-Flt-1 antibody, or antigen-binding fragment thereof, is relative to CD31 staining measured in the muscle of mice administered an isotype control antibody. For example, the normalized CD31 percent positivity in the diaphragm muscle of mice administered the anti-Flt-1 antibody, or antigen-binding fragment thereof may be at least about 200%, about 190%, about 180%, about 170%, about 160%, about 150%, about 140%, about 130%, about 120% or about 110%. In a further example, the normalized CD31 percent positivity in the TA muscle of mice administered the anti-Flt-1 antibody, or antigen-binding fragment thereof may be at least about 300%, about 290%, about 280%, about 270%, about 260%, about 250%, about 240%, about 230%, about 220%, about 210%, about 200%, about 190%, about 180%, about 170%, about 160%, about 150%, about 140%, about 130%, about 120% or about 110%, and ranges therein.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof selectively binds human Flt-1, and has minimal or no appreciable binding to other mammalian Flt-1 receptors (e.g., with a binding affinity less than 10⁻⁷M or 10⁻⁶M). In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof selectively binds human Flt-1 and does not bind to monkey Flt-1. In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof selectively binds human Flt-1 and does not bind to mouse Flt-1.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof binds human Flt-1 as well as monkey Flt-1. In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof binds to cynomolgus Flt-1. In some embodiments an anti-Flt-1 antibody, or antigen-binding fragment thereof binds human Flt-1 as well as mouse Flt-1.

In some embodiments, an anti-Flt-1 antibody, or antigen-binding fragment thereof, is selected from the group consisting of IgG, F(ab′)₂, F(ab)₂, Fab′, Fab, ScFvs, diabodies, triabodies and tetrabodies.

In some embodiments an anti-Flt-1 antibody, or antigen-binding fragment thereof, is IgG. In some embodiments an anti-Flt-1 antibody, or antigen-binding fragment thereof, is IgG1.

Engineered Constant Regions

In some embodiments, a suitable anti-Flt-1 antibody contains an Fc domain or a portion thereof that binds to the FcRn receptor. As a non-limiting example, a suitable Fc domain may be derived from an immunoglobulin subclass such as IgG. In some embodiments, a suitable Fc domain is derived from IgG1, IgG2, IgG3, or IgG4. Particularly suitable Fc domains include those derived from human or humanized antibodies.

It is contemplated that improved binding between Fc domain and the FcRn receptor results in prolonged serum half-life. Thus, in some embodiments, a suitable Fc domain (SEQ ID NO:104) comprises one or more amino acid mutations that lead to improved binding to FcRn. Various mutations within the Fc domain that effect improved binding to FcRn are known in the art and can be adapted to practice the present invention. In some embodiments, a suitable Fc domain comprises one or more mutations at one or more positions corresponding to Leu 234, Leu 235, Gly 237, Thr 250, Met 252, Ser 254, Thr 256, Thr 307, Glu 380, Met 428, His 433, and/or Asn 434 of human IgG1.

Some mutations in the Fc domain lead to reduced binding of the IgG with the FcRn receptor and thereby inhibit effector function. In some embodiments, a suitable Fc domain (SEQ ID NO:104) comprises one or more mutations at one or more positions corresponding to Leu 234, Leu 235 and Gly 237 of human IgG1. In a particular embodiment Leu 234 is mutated to Ala. In another embodiment Leu 235 is mutated to Ala. In yet another embodiment, Gly 237 is mutated to Ala.

In some embodiments, an anti-FLT-1 antibody or antigen-binding fragment contains a spacer and/or is linked to another entity. In some embodiments, the linker or spacer comprises a sequence at least 50% (e.g., at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100%) identical to GAPGGGGGAAAAAGGGGGGAP (SEQ ID NO:105) (GAG linker). In some embodiments, the linker or spacer comprises a sequence at least 50% (e.g., at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100%) identical to GAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAP (SEQ ID NO:106) (GAG2 linker). In some embodiments, the linker or spacer comprises a sequence at least 50% (e.g., at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100%) identical to

(GAG3 linker) (SEQ ID NO: 107) GAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAG GGGGGAP.

Production of Anti-Flt-1 Antibodies and Antigen-Binding Fragments

A recombinant anti-Flt-1 antibody or antigen-binding fragment thereof, suitable for the present invention may be produced by any available means. For example, a recombinant anti-Flt-1 antibody or antigen-binding fragment may be recombinantly produced by utilizing a host cell system engineered to express a recombinant anti-Flt-1 antibody or antigen-binding fragment-encoding nucleic acid.

Thus, the present invention further provides polynucleotide sequences encoding the various amino acid sequences described herein. In some embodiments, the present invention provides a polynucleotide sequence encoding an anti-Flt-1 antibody heavy chain or light chain amino acid sequence described herein, for example, any one of SEQ ID NOs:62-86 or SEQ ID NOs:108-110. In some embodiments, the present invention provides a polynucleotide sequence encoding a variable region of an anti-Flt-1 antibody heavy chain or light chain amino acid sequence described herein, for example, any one of SEQ NOs:35-61. In some embodiments, the present invention provides a polynucleotide sequence encoding a CDR region of an anti-Flt-1 antibody heavy chain or light chain amino acid sequence described herein, for example, any one of SEQ ID NOs:1-34. In some embodiments, the present invention provides a polynucleotide sequence encoding an anti-Flt-1 antibody constant region amino acid sequence described herein, for example, any one of SEQ ID NO:87-89. In some embodiments, the present invention provides a polynucleotide sequence encoding an anti-Flt-1 antibody Fc region amino acid sequence described herein, for example, SEQ ID NO:104. In some embodiments, the present invention provides a polynucleotide sequence encoding an anti-Flt-1 antibody linker amino acid sequence described herein, for example, SEQ ID NOs:105-107.

In some embodiments, a polynucleotide sequence encoding an anti-Flt-1 antibody heavy chain, light chain, variable region, CDR region, Fc region or linker region amino acid sequence further includes a sequence encoding a signal peptide. As a non-limiting example, a suitable signal peptide includes amino acid sequence MGWSCIILFLVATATGVHS (SEQ ID NO:111).

Various polynucleotide sequences described herein may be embodied in various vector systems for expression of recombinant anti-Flt-1 antibodies or antigen-binding fragment thereof.

Where antibodies are recombinantly produced, any expression system can be used. To give but a few examples, known expression systems include, for example, egg, baculovirus, plant, yeast, or mammalian cells.

In some embodiments, a recombinant anti-Flt-1 antibody or antigen-binding fragment thereof suitable for the present invention are produced in mammalian cells. Non-limiting examples of mammalian cells that may be used in accordance with the present invention include BALB/c mouse myeloma line (NSO/l, ECACC No: 85110503); human retinoblasts (PER.C6, CruCell, Leiden, The Netherlands); and monkey kidney CV1 line transformed by SV40 (COS-7, ATCC CRL 1651).

In some embodiments, the present invention provides a recombinant anti-Flt-1 antibody or antigen-binding fragment thereof produced from human cells. In some embodiments, the present invention provides an anti-Flt-1 antibody or antigen-binding fragment thereof produced from CHO cells.

Pharmaceutical Compositions Containing the Antibodies of the Invention

The present invention further provides pharmaceutical compositions comprising therapeutically active ingredients in accordance with the invention (e.g. anti-Flt-1 antibody, or antigen-binding fragment thereof), together with one or more pharmaceutically acceptable carrier or excipient. Such pharmaceutical compositions may optionally comprise one or more additional therapeutically-active substances.

Although the descriptions of pharmaceutical compositions provided herein are principally directed to pharmaceutical compositions which are suitable for ethical administration to humans, it will be understood by the skilled artisan that such compositions are generally suitable for administration to animals of all sorts. Modification of pharmaceutical compositions suitable for administration to humans in order to render the compositions suitable for administration to various animals is well understood, and the ordinarily skilled veterinary pharmacologist can design and/or perform such modification with merely ordinary, if any, experimentation.

Formulations of the pharmaceutical compositions described herein may be prepared by any method known or hereafter developed in the art of pharmacology. In general, such preparatory methods include the step of bringing the active ingredient into association with a diluent or another excipient or carrier and/or one or more other accessory ingredients, and then, if necessary and/or desirable, shaping and/or packaging the product into a desired single- or multi-dose unit.

A pharmaceutical composition in accordance with the invention may be prepared, packaged, and/or sold in bulk, as a single unit dose, and/or as a plurality of single unit doses. As used herein, a “unit dose” is discrete amount of the pharmaceutical composition comprising a predetermined amount of the active ingredient. The amount of the active ingredient is generally equal to the dosage of the active ingredient which would be administered to a subject and/or a convenient fraction of such a dosage such as, for example, one-half or one-third of such a dosage.

Relative amounts of the active ingredient, the pharmaceutically acceptable excipient or carrier, and/or any additional ingredients in a pharmaceutical composition in accordance with the invention will vary, depending upon the identity, size, and/or condition of the subject treated and further depending upon the route by which the composition is to be administered. By way of example, the composition may comprise between 0.1% and 100% (w/w) active ingredient.

Pharmaceutical formulations may additionally comprise a pharmaceutically acceptable excipient or carrier, which, as used herein, includes any and all solvents, dispersion media, diluents, or other liquid vehicles, dispersion or suspension aids, surface active agents, isotonic agents, thickening or emulsifying agents, preservatives, solid binders, lubricants and the like, as suited to the particular dosage form desired. Remington's The Science and Practice of Pharmacy, 21^(st) Edition, A. R. Gennaro (Lippincott, Williams & Wilkins, Baltimore, Md., 2006; incorporated herein by reference) discloses various excipients used in formulating pharmaceutical compositions and known techniques for the preparation thereof. Except insofar as any conventional excipient medium or carrier is incompatible with a substance or its derivatives, such as by producing any undesirable biological effect or otherwise interacting in a deleterious manner with any other component(s) of the pharmaceutical composition, its use is contemplated to be within the scope of this invention.

In some embodiments, a pharmaceutically acceptable excipient or carrier is at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% pure. In some embodiments, an excipient or carrier is approved for use in humans and for veterinary use. In some embodiments, an excipient or carrier is approved by United States Food and Drug Administration. In some embodiments, an excipient or carrier is pharmaceutical grade. In some embodiments, an excipient or carrier meets the standards of the United States Pharmacopoeia (USP), the European Pharmacopoeia (EP), the British Pharmacopoeia, and/or the International Pharmacopoeia.

Pharmaceutically acceptable excipients or carriers used in the manufacture of pharmaceutical compositions include, but are not limited to, inert diluents, dispersing and/or granulating agents, surface active agents and/or emulsifiers, disintegrating agents, binding agents, preservatives, buffering agents, lubricating agents, and/or oils. Such excipients or carriers may optionally be included in pharmaceutical formulations. Excipients or carriers such as cocoa butter and suppository waxes, coloring agents, coating agents, sweetening, flavoring, and/or perfuming agents can be present in the composition, according to the judgment of the formulator.

Suitable pharmaceutically acceptable excipients or carriers include but are not limited to water, salt solutions (e.g., NaCl), saline, buffered saline, alcohols, glycerol, ethanol, gum arabic, vegetable oils, benzyl alcohols, polyethylene glycols, gelatin, carbohydrates such as lactose, amylose or starch, sugars such as mannitol, sucrose, or others, dextrose, magnesium stearate, talc, silicic acid, viscous paraffin, perfume oil, fatty acid esters, hydroxymethylcellulose, polyvinyl pyrolidone, etc., as well as combinations thereof. The pharmaceutical preparations can, if desired, be mixed with auxiliary agents (e.g., lubricants, preservatives, stabilizers, wetting agents, emulsifiers, salts for influencing osmotic pressure, buffers, coloring, flavoring and/or aromatic substances and the like) which do not deleteriously react with the active compounds or interfere with their activity. In a preferred embodiment, a water-soluble carrier suitable for intravenous administration is used.

A suitable pharmaceutical composition or medicament, if desired, can also contain minor amounts of wetting or emulsifying agents, or pH buffering agents. A composition can be a liquid solution, suspension, emulsion, tablet, pill, capsule, sustained release formulation, or powder. A composition can also be formulated as a suppository, with traditional binders and carriers such as triglycerides. Oral formulations can include standard carriers such as pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, polyvinyl pyrollidone, sodium saccharine, cellulose, magnesium carbonate, etc.

A pharmaceutical composition or medicament can be formulated in accordance with the routine procedures as a pharmaceutical composition adapted for administration to human beings. For example, in some embodiments, a composition for intravenous administration typically is a solution in sterile isotonic aqueous buffer. Where necessary, the composition may also include a solubilizing agent and a local anesthetic to ease pain at the site of the injection. Generally, the ingredients are supplied either separately or mixed together in unit dosage form, for example, as a dry lyophilized powder or water free concentrate in a hermetically sealed container such as an ampule or sachette indicating the quantity of active agent. Where the composition is to be administered by infusion, it can be dispensed with an infusion bottle containing sterile pharmaceutical grade water, saline or dextrose/water. Where the composition is administered by injection, an ampule of sterile water for injection or saline can be provided so that the ingredients may be mixed prior to administration.

General considerations in the formulation and/or manufacture of pharmaceutical agents may be found, for example, in Remington: The Science and Practice of Pharmacy 21^(st) ed., Lippincott Williams & Wilkins, 2005 (incorporated herein by reference).

Routes of Administration

An anti-Flt-1 antibody or antigen-binding fragment thereof described herein (or a composition or medicament containing an anti-Flt-1 antibody or antigen-binding fragment thereof described herein) is administered by any appropriate route. In some embodiments, an anti-Flt-1 antibody or antigen-binding fragment protein or a pharmaceutical composition containing the same is administered parenterally. Parenteral administration may be intravenous, intradermal, intrathecal, inhalation, transdermal (topical), intraocular, intramuscular, subcutaneous, intramuscular, and/or transmucosal administration. In some embodiments, an anti-Flt-1 antibody or antigen-binding fragment thereof or a pharmaceutical composition containing the same is administered subcutaneously. As used herein, the term “subcutaneous tissue”, is defined as a layer of loose, irregular connective tissue immediately beneath the skin. For example, the subcutaneous administration may be performed by injecting a composition into areas including, but not limited to, the thigh region, abdominal region, gluteal region, or scapular region. In some embodiments, an anti-Flt-1 antibody or antigen-binding fragment thereof or a pharmaceutical composition containing the same is administered intravenously. In some embodiments, an anti-Flt-1 antibody or antigen-binding fragment thereof or a pharmaceutical composition containing the same is administered orally. More than one route can be used concurrently, if desired.

In some embodiments, administration results only in a localized effect in an individual, while in other embodiments, administration results in effects throughout multiple portions of an individual, for example, systemic effects. Typically, administration results in delivery of an anti-Flt-1 antibody or antigen-binding fragment to one or more target tissues including but not limited to kidney, liver, brain, spinal cord, intestinal tract, eye, lung, spleen, heart, including cardiac muscle, striated muscle, and smooth muscle.

In some embodiments, striated muscle is selected from the group consisting of triceps, tibialis anterior, soleus, gastrocnemius, quadriceps, and diaphragm.

In some embodiments, the smooth muscle is the muscles lining blood vessels, bronchioles, bladder, and gastrointestinal tract such as rectum.

Dosage Forms and Dosing Regimen

In some embodiments, a composition is administered in a therapeutically effective amount and/or according to a dosing regimen that is correlated with a particular desired outcome (e.g., with treating or reducing risk for a muscular dystrophy, such as Duchenne muscular dystrophy).

Particular doses or amounts to be administered in accordance with the present invention may vary, for example, depending on the nature and/or extent of the desired outcome, on particulars of route and/or timing of administration, and/or on one or more characteristics (e.g., weight, age, personal history, genetic characteristic, lifestyle parameter, severity of cardiac defect and/or level of risk of cardiac defect, etc., or combinations thereof). Such doses or amounts can be determined by those of ordinary skill. In some embodiments, an appropriate dose or amount is determined in accordance with standard clinical techniques. Alternatively or additionally, in some embodiments, an appropriate dose or amount is determined through use of one or more in vitro or in vivo assays to help identify desirable or optimal dosage ranges or amounts to be administered.

In various embodiments, an anti-Flt-1 antibody or antigen-binding fragment thereof is administered at a therapeutically effective amount. Generally, a therapeutically effective amount is sufficient to achieve a meaningful benefit to the subject (e.g., treating, modulating, curing, preventing and/or ameliorating the underlying disease or condition). In some particular embodiments, appropriate doses or amounts to be administered may be extrapolated from dose-response curves derived from in vitro or animal model test systems.

In some embodiments, a provided composition is provided as a pharmaceutical formulation. In some embodiments, a pharmaceutical formulation is or comprises a unit dose amount for administration in accordance with a dosing regimen correlated with achievement of the reduced incidence or risk of a muscular dystrophy, such as Duchenne muscular dystrophy.

In some embodiments, a formulation comprising an anti-Flt-1 antibody or antigen-binding fragment described herein administered as a single dose. In some embodiments, a formulation comprising an anti-Flt-1 antibody or antigen-binding fragment described herein is administered at regular intervals. Administration at an “interval,” as used herein, indicates that the therapeutically effective amount is administered periodically (as distinguished from a one-time dose). The interval can be determined by standard clinical techniques. In some embodiments, a formulation comprising an anti-Flt-1 antibody or antigen-binding fragment described herein is administered bimonthly, monthly, twice monthly, triweekly, biweekly, weekly, twice weekly, thrice weekly, daily, twice daily, or every six hours. The administration interval for a single individual need not be a fixed interval, but can be varied over time, depending on the needs of the individual. In a particular embodiment the anti-Flt-1 antibody, or antigen-binding fragment thereof is administered twice weekly.

As used herein, the term “bimonthly” means administration once per two months (i.e., once every two months); the term “monthly” means administration once per month; the term “triweekly” means administration once per three weeks (i.e., once every three weeks); the term “biweekly” means administration once per two weeks (i.e., once every two weeks); the term “weekly” means administration once per week; and the term “daily” means administration once per day.

In some embodiments, a formulation comprising an anti-Flt-1 antibody or antigen-binding fragment described herein is administered at regular intervals indefinitely. In some embodiments, a formulation comprising an anti-Flt-1 antibody or antigen-binding fragment described herein is administered at regular intervals for a defined period.

As described herein, the term “therapeutically effective amount” is largely determined based on the total amount of the therapeutic agent contained in the pharmaceutical compositions of the present invention. A therapeutically effective amount is commonly administered in a dosing regimen that may comprise multiple unit doses. For any particular composition, a therapeutically effective amount (and/or an appropriate unit dose within an effective dosing regimen) may vary, for example, depending on route of administration or on combination with other pharmaceutical agents.

In some embodiments, the anti-Flt-1 antibody, or antigen-binding fragment thereof is administered at a dose ranging from about 0.1 mg/kg to about 50 mg/kg. In other embodiments the anti-Flt-1 antibody, or antigen-binding fragment thereof is administered at a dose ranging from about 0.1 mg/kg to about 40 mg/kg, from about 0.1 mg/kg to about 30 mg/kg, from about 0.1 mg/kg to about 20 mg/kg, from about 0.1 mg/kg to about 10 mg/kg, from about 0.1 mg/kg to about 5 mg/kg, from about 0.1 mg/kg to about 3 mg/kg, from about 0.1 mg/kg to about 1 mg/kg, from about 1.0 mg/kg to about 40 mg/kg, from about 1.0 mg/kg to about 30 mg/kg, from about 1.0 mg/kg to about 20 mg/kg, from about 1.0 mg/kg to about 10 mg/kg, from about 1.0 mg/kg to about 5 mg/kg or from about 1.0 mg/kg to about 3 mg/kg. In particular embodiments, the anti-Flt-1 antibody, or antigen-binding fragment thereof is administered at a dose of about 1.0 mg/kg, about 3.0 mg/kg, about 10 mg/kg or about 20 mg/kg.

In some embodiments, administration of an anti-Flt-1 antibody, or antigen-binding fragment thereof reduces the intensity, severity, or frequency, or delays the onset of at least one DMD sign or symptom. In some embodiments administration of an anti-Flt-1 antibody, or antigen-binding fragment thereof reduces the intensity, severity, or frequency, or delays the onset of at least one DMD sign or symptom selected from the group consisting of muscle wasting, skeletal deformation, cardiomyopathy, muscle ischemia, cognitive impairment, and impaired respiratory function.

In some embodiments, administration of an anti-Flt-1 antibody, or antigen-binding fragment thereof improves clinical outcome as measured by a 6 minute walk test, quantitative muscle strength test, timed motor performance test. Brooke and Vignos limb function scales, pulmonary function test (forced vital capacity, forced expiratory volume in 1 second, peak expiratory flow rate, maximal inspiratory and expiratory pressures), health-related quality of life, knee and elbow flexors, elbow extensors, shoulder abduction, grip strength, time to rise from supine position, North Start Ambulatory Assessment, timed 10 meter walk/run, Egen-Klassification scale, Gowers score, Hammersmith motor ability, hand held myometry, range of motion, goniometry, hypercapnia, Nayley Scales of Infant and Toddler Development, and/or a caregiver burden scale.

Combination Therapy

In some embodiments, an anti-Flt-1 antibody or antigen-binding fragment thereof is administered in combination with one or more additional therapeutic agents. In one embodiment the additional therapeutic agent is a corticosteroid, e g., prednisone. In another embodiment, the additional therapeutic agent is a glucocorticoid, e.g., deflazacort. In another embodiment, the additional therapeutic agent is follistatin or a recombinant protein thereof. In another embodiment the additional therapeutic agent is an RNA modulating therapeutic. The RNA modulating therapeutic may be an exon-skipping therapeutic or gene therapy. The RNA modulating therapeutic may be, for example, Drispersen, PRO044, PRO045, Eteplirsen (AVI-4658), SRP-4053, SRP-4045, SRP-4050, SRP-4044, SRP-4052, SRP-4055 or SRP-4008. In some embodiments the additional therapeutic agent is currently used for treatment of a muscular dystrophy. In other embodiments the additional therapeutic agent may also be used to treat other diseases or disorders. In some embodiments, the known therapeutic agent(s) is/are administered according to its standard or approved dosing regimen and/or schedule. In some embodiments, the known therapeutic agent(s) is/are administered according to a regimen that is altered as compared with its standard or approved dosing regimen and/or schedule. In some embodiments, such an altered regimen differs from the standard or approved dosing regimen in that one or more unit doses is altered (e.g., reduced or increased) in amount, and/or in that dosing is altered in frequency (e.g., in that one or more intervals between unit doses is expanded, resulting in lower frequency, or is reduced, resulting in higher frequency).

EXAMPLES Example 1. Generation and Characterization of High Affinity Anti-Flt-1 Antibodies

Generation of Antibodies

Monoclonal antibodies were generated against soluble Flt-1 using llama monoclonal antibody methodology. Briefly, llamas were immunized with recombinant human soluble Flt-1 (purchased from ABCAM) and the serum was collected.

Antibody Characterization

Antibodies that bound to human and mouse Flt-1 were further characterized for 1) VH family; 2) affinity for Flt-1; 3) IC50; 4) off-rate screening by Biacore assay, 5) cross-reactivity to cynomolgus Flt-1 and 6) binding to VEGF R2 and VEGF R3. Candidate antibodies against human Flt-1 (hFl-1) and mouse Flt-1 (mFlt-1) were characterized as shown in Table 4.

TABLE 4 IC50 by Bioassay Human VH Affinity (nM) ELISA (pM) (% rescue) identity (%) Antibody family hFlt-1 mFlt-1 hFlt-1 mFlt-1 hFlt-1 mFlt-1 VH VL 13B4 15 0.6 1.4 13.3 500 >90 72.2 94.3 93.7 10G12 17 0.29 0.33 400 300 44 87.5 90.8 81 11A11 20 0.2 33.3 >90 90.8 91.1

Pharmacokinetic properties of antibody 13B4 and 10G12 were studied in mice by intravenous administration of 10 mg/kg of each antibody (Table 5). The data demonstrated that antibody 10G12 cannot be detected beyond 288 hours, while antibody 13B4 can be detected at 672 hours (FIGS. 1A-1B).

TABLE 5 Cmax Tmax AUC_(0-last) AUC_(0-inf) CL Antibody t_(1/2) (h) (ng/ml) (hr) (hr*ng/ml) (hr*ng/ml) (ml/hr/kg) R² 13B4 87.7 293675 1 31669464 31926743 0.31 0.960 10G12 99.3 359268 0.5 15999900 19120025 0.52 0.944

In Vivo Efficacy of Antibodies

Mdx mice (i.e., a mouse model of Duchenne muscular dystrophy) were treated with 20 mg/kg of either antibody 13B4 or antibody 10G12 by intravenous administration twice a week for one month beginning at 4 weeks of age. Control mice were treated with vehicle only, an isotype control antibody that does not bind to Flt-1 or a commercial anti-Flt-1 antibody known as Flt-1:VEGF antagonist (Angio Proteomie, catalog number AP-MAB0702). To assess serum antibody concentration at a trough exposure point, blood was collected 4 days after the fifth intravenous dose. To assess serum antibody concentration at a peak exposure point, blood was collected 24 hours after the last dose. Peak and trough concentration of antibodies 13B4 and 10G12 are shown in FIGS. 2A and 2B. The concentration of free antibody 13B4 and free antibody 10G12 in blood was higher than that of the isotype control antibody and the commercial control antibody at both the peak and trough exposure time points.

To assess serum free sFlt-1 levels and VEGF levels, blood was collected 24 hours after the fifth intravenous dose and prior to sacrifice. Administration of antibody 13B4 and antibody 10G12, as well as the commercial control antibody, significantly decreased the serum concentration on sFlt-1 (p<0.0001) as compared to the isotype control antibody (FIG. 3). Administration of antibody 13B4 and antibody 10G12, resulted in a significant increase in serum levels of VEGF as compared to the isotype control antibody (p<0.001) (FIG. 4). Administration of the commercial control antibody also resulted in a significant increase in blood levels of VEGF as compared to the isotype control antibody (p<0.05) (FIG. 4).

Histopathology

Mice were sacrificed at the end of the 30 day treatment period and the diaphragm muscle and tibialis anterior (TA) muscle were collected and sectioned to determine if the anti-Flt-1 antibodies induced angiogenesis in skeletal muscle. Sections of muscle were stained with the endothelial cell marker CD31. A significant increase in capillary density was seen in the diaphragms of mice treated with antibody, 13B4, 10G12 or the commercial control antibody as compared to the diaphragms of mice treated with the isotype control antibody (FIGS. 5A-5D). The data were quantified using automated quantitative imaging software as shown in FIGS. 6A-6B. There was a significant increase in the CD31 positive area in diaphragms of mice treated with the commercial control antibody (p<0.05), antibody 13B4 (p<0.01) and antibody 10G12 (p<0.0001) as compared to the diaphragms of mice treated with the isotype control antibody. A significant increase in the CD31 positive area of the tibialis anterior (TA) muscle of mice treated with antibody 10G12 (p<0.01) as compared to the tibialis anterior muscle of mice treated with the isotype control antibody was also demonstrated.

This studies demonstrated that administration of an Flt-1 antibody (e.g., 10G12 and 13B4) to mdx mice resulted in a significant increase in endothelial cell proliferation as well as a decrease in soluble Flt-1 in serum and an increase in serum VEGF concentrations. These antibodies demonstrated binding affinity for the Flt-1 target in the pM range (see Table 4), IC50 for Flt-1 binding of less than 100 pM (see Table 4) and greater than 50% rescue of VEGF signaling in a bioassay.

Example 2. Generation and Characterization of High Affinity Anti-Flt-1 Antibodies

Additional anti-Flt-1 monoclonal antibodies were generated as described above. These antibodies were further characterized for binding affinity to sFlt-1 antigen (by ELISA and Biacore), competition for VEGF in a sFlt-1:VEGF competition ELISA; and performance in a cell based assay.

Antibody Characterization—Binding to Target

The monoclonal anti-Flt-1 antibodies were assayed for binding to recombinant sFlt-1 antigen in an ELISA assay (FIG. 7). All antibodies demonstrated a dose-dependent increase in binding. Binding affinity of the anti-Flt-1 antibodies to mouse and human Flt-1 antigen was measured by surface plasmon resonance methodology (i.e., Biacore) (Table 6). The antibodies bound to human Flt-1 in the nanomolar range with antibody 11A11 demonstrating the highest binding affinity for human Flt-1. Biacore analysis also demonstrated that the antibodies did not cross-react with VEGF R2 or VEGF R3 (Table 6), however all antibodies did cross react with cynomolgus Flt-1.

TABLE 6 Affinity (nM) Binding Family Human Mouse VEGFR2 VEGFR3 13B4 15 0.58 1.4 — — 10G2 1.5 1.4 — — 10G5 1.6 4.2 — — 18H2 1.8 3.2 — — 18A10 1.2 2 — — 18C5 2.7 9.2 — — 18C12 1.4 2 — — 18B6 21 1.7 1.2 — — 16B3 19 2.7 3 — — 10G12 17 3.1 6.9 — — 16B12 18 2.7 5.7 — — Angio 2.3 8.2 11A11 20 0.16 — —

Antibody Characterization—Competition/Antagonism

To estimate the potency of the antibodies, the antibodies were assay in a competition ELISA using human sFlt-1 and VEGF. Antibody concentrations tested ranged from 0.1 mg/mL to 10,000 ng/mL. The commercial anti-Flt-1 antibody served as a control. With the exception of 11A11, all antibodies were able to prevent binding of VEGF to sFlt-1 (FIG. 8).

Antibody Characterization—Cell Based Assay

Human primary vein endothelial cells (HUVECs) were stimulated with VEGF in the presence of sFlt-1 and monoclonal antibodies 02G07, 11A11 and 13B4. VEGF induced activation of cells was assayed by determining the phosphorylation status of the VEGF R2 receptor. The data are expressed as a percent rescue of the phosphorylation of the VEGF R2 receptor relative to the phosphorylation of the VEGF R2 receptor in the presence of sFlt-1 alone (e.g., without anti-Flt-1 antibodies). The monoclonal antibodies rescued cell activation (i.e., phosphorylation) by antagonizing soluble Flt-1 (FIG. 9).

Example 3. Characterization of High Affinity Anti-Flt-1 Antibodies Generated by Light Chain Shuffling

Light chain shuffling of antibodies 18B6, 11A11 and 13B4 described in Example 2 was performed to increase the affinity and potency of the candidate antibodies.

Antibody Characterization—Binding to Target

The resulting antibodies displayed increased affinity for the Flt-1 antigen. For instance the K_(D) of antibody 21C6 increased approximately 10-fold over that of the parent antibody, 11A11. Similarly, the K_(D) of antibody 21B3 increased approximately 5-fold over that of the parent antibody, 13B4 (Table 7).

TABLE 7 ka (1/Ms) kd (1/s) KD (M) 18B6 3.95E+05 3.25E−04 8.22E−10 24A8 2.24E+05 1.35E−04 6.05E−10 21F9 2.84E+05 2.42E−04 8.52E−10 11A11 3.17E+05 5.32E−05 1.68E−10 21C6 1.31E+06 2.62E−05 2.00E−11 21B6 7.59E+05 6.50E−05 8.57E−11 13B4 4.16E+05 1.62E−04 3.89E−10 21B3 5.58E+05 4.73E−05 8.48E−11 21A1 2.23E+05 1.15E−04 5.16E−10 21D1 8.44E+05 1.44E−04 1.71E−10 21B4 4.96E+05 1.58E−04 3.19E−10 19H6 3.32E+05 1.09E−04 3.29E−10

Antibody characterization—Competition/Antagonism

To estimate the potency of the antibodies following the light chain shuffling, the antibodies were assay in a competition ELISA using human sFlt-1 and VEGF. Antibody concentrations tested ranged from 0.2 mg/mL to 200 ng/mL. The ability of parent antibody 13B4 to competitively bind sFlt-1 was compared to that of antibodies generated by light chain shuffling. All antibodies demonstrated a dose dependent inhibition of binding of VEGF to human sFlt-1 with clone 21B3 the most effective competitor (FIG. 10).

In Vivo Efficacy

To determine the serum half-life and pharmacokinetic characteristics of the light chain shuffled antibodies, mice were administered a single 10 mg/kg dose of light chain shuffled antibodies 27H9 and 21B3 and parent antibody 13B4 each labeled with I¹²⁵. Serum was collected at 0.083, 0.25, 0.5, 1, 4, 8, and 24 hours and at 3, 5, 7, 14, 21 and 28 days and the serum concentration of the antibodies determined. The serum half-life was reduced in the light shuffled antibodies as compared to the parent antibody (FIG. 11). However, the light chain shuffled antibodies showed improved pharmacodynamic characteristics as compared to the parent. For instance, antibody 27H9 reached a maximum concentration of 222.4 ug/mL by 0.083 hours whereas the parent antibody 13B4 reached a maximum concentration of 217 ug/mL by 0.5 hours (Table 8).

TABLE 8 T½ Cmax Tmax AUC0-last AUC 0-inf Vss Cl V0 TA (hr) (ug/ml) (hr) (hr*ug/ml) (hr*ug/ml) (ml/kg) (ml/hr/kg) (ml/kg) R2 13B4 129.4 217.3 0.5 27044 27798 71 0.36 48.7 0.97 21B3 56.5 215.8 0.083 12590 12602 73 0.79 42.9 0.95 27H9 62.8 222.4 0.083 14318 14329 68 0.7 44.3 0.96

Histopathology

To determine if the light chain shuffled and parent antibodies could induce endothelial cell proliferation, mdx mice were treated with 20 mg/kg of antibody biweekly for 4 weeks by intravenous administration. Mice were sacrificed at the end of the treatment period and the diaphragm and tibialis anterior muscles were collected and sectioned to determine if the antibodies induced angiogenesis in skeletal muscle. Sections of muscle were stained with the endothelial cell marker CD31. A significant increase in capillary density in the diaphragm was seen in the mice treated with antibody 13B4 and 21B3 as compared to the diaphragms of mice treated with the isotype control antibody (FIGS. 12A-12C). In addition, there was a significant increase in capillary density in the tibialis anterior from mice treated with the light chain shuffled antibody 21B3 as compared to the tibialis anterior muscle from mice treated with the isotype control antibody (FIGS. 12D-12F).

The biodistribution of antibodies 27H9, 13B4 and 21B3 in the diaphragm, tibialis and gastrocnemius muscles was determined using ¹²⁵I labeled antibodies. The diaphragm showed the highest exposure for all antibodies over the time course (FIGS. 13A-13C).

These studies demonstrated that administration of an Flt-1 antibody (i.e., 13B4 and 21B3) to mdx mice resulted in a significant increase in endothelial cell proliferation.

Example 4. In Vivo Efficacy of High Affinity Anti-Flt-1 Antibody 21B3

Mdx mice were treated with 1, 3, 10 or 20 mg/kg of antibody 21B3, or 20 mg/kg of an isotype control antibody, by intravenous administration twice a week for one month beginning at 4 weeks of age. To assess serum antibody concentration at a trough exposure point, blood was collected 4 days after the fifth intravenous dose. To assess blood antibody concentration at a peak exposure point, blood was collected 24 hours after the last dose. Peak and trough serum concentrations of antibody 21B3 and the isotype control antibody are shown in FIGS. 14A and 14B. The peak and trough levels of antibody 21B3 were dose dependent and higher than the isotype control antibody.

To assess serum levels of free sFlt-1, blood was collected on days 0, 14 and 28. Administration of antibody 21B3 induced a dose dependent decrease in serum free sFlt-1 levels. The response was more durable at the 10 and 20 mg/kg doses as seen at both day 14 and day 28. However, a statistically significant decrease was observed is free sFlt-1 levels at the 3, 10 and 20 mg/kg doses as compared to the free sFlt-1 level in mice treated with vehicle alone (FIG. 15).

To assess serum levels of VEGF, blood was collected on days 0, 14 and 28. Administration of antibody 21B3 induced a dose dependent increase in serum VEGF levels. As observed for the free sFlt-1 levels, the response was more durable at the 10 and 20 mg/kg doses and at both day 14 and day 28. In fact, a statistically significant increase in serum VEGF was observed at the 10 and 20 mg/kg doses of antibody 21B3 as compared to serum VEGF levels in mice treated with vehicle alone (FIG. 16).

Histopathology

Mice were sacrificed at the end of the 30 day treatment period and the diaphragm and tibialis anterior muscles were collected and sectioned to determine if the anti-Flt-1 antibody induced angiogenesis in skeletal muscle. Sections of muscle were stained for the endothelial cell marker CD31. A significant increase in capillary density in the diaphragm muscles of mice treated with antibody 21B3 was seen as compared to the capillary density in the diaphragm muscles of mice treated with the isotype control antibody (FIGS. 17A-17E). The data were quantified using automated quantitative imaging software as shown in FIG. 18. There was a significant increase in the CD31 positive area in the diaphragm muscles of mice treated with 10 mg/kg or 20 mg/kg (p<0.0001) as compared to the CD31 positive area in the diaphragm muscles of mice treated isotype control antibody.

A significant increase in the capillary density in the tibialis anterior muscle was also seen in the mice treated with antibody 21B3 as compared to the tibialis anterior muscle in mice treated with the isotype control antibody (FIGS. 19A-19E). The data were quantified using automated quantitative imaging software as shown in FIG. 20. There was a significant increase in the CD31 positive area in the tibialis anterior muscle of mice treated with 10 mg/kg or 20 mg/kg (p<0.0001) as compared to the CD31 positive area in the tibialis anterior muscle of mice treated with isotype control antibody.

RP-LC/MS Characterization

The molecular weight of the deglycosylated 21B3 antibody was determined by reverse phase liquid chromatography/mass spectrometry (RP-LC/MS) (FIG. 21A). Following a reduction reaction, the molecular weight of the light chain and the heavy chain were determined. The glycosylation pattern of the heavy chain was also determined (FIG. 21B).

These results demonstrated that administration of an Flt-1 antibody (i.e., 21B3) to mdx mice resulted in a significant increase in endothelial cell proliferation as well as a decrease in soluble Flt-1 in serum and an increase in VEGF concentrations in serum.

Example 5. Characterization of Humanized High Affinity Anti-Flt-1 Antibodies

Light chain shuffled antibodies described in Example 3 were further modified to introduce sequence variation in the CDR regions and or Fc effector regions. These antibodies were evaluated by a surface plasmon resonance methodology (e.g., Biacore) to determine the binding characteristics (Table 9). Antibody 27H9 NG/NA AAA demonstrated an approximately 2 fold reduced binding affinity for Flt-1.

TABLE 9 ka (1/Ms) kd (1/s) Rmax (RU) KD (M) Chi² EXP 21B3 WT 5.4E+05 1.7E−04 292 3.2E−10 290 2 21B3 AAA 5.2E+05 1.1E−04 305 2.1E−10 371 2 27H9 old 07/05 3.5E+05 7.9E−05 306 2.3E−10 235 1 27H9 WT 23/07 3.3E+05 8.4E−05 323 2.6E−10 236 1 27H9 NG/QG 3.7E+05 1.3E−04 315 3.6E−10 280 1 27H9 NG/NA 2.9E+05 1.1E−04 298 3.9E−10 158 1 27H9 NG/NA 2.9E+05 1.5E−04 240 5.1E−10 96.4 2 27H9 NG/NA AAA 2.9E+05 1.5E−04 236 5.1E−10 72.5 2

The antibodies were also evaluated in the cell based assay for ability to rescue cell activation by antagonizing sFlt-1. Human primary vein endothelial cells (HUVECs) were stimulated with VEGF in the presence of sFlt-1 and the monoclonal antibodies. VEGF induced activation of cells was assayed by determining the phosphorylation status of the VEGF R2 receptor. The monoclonal antibodies rescued cell activation (i.e., phosphorylation) by antagonizing soluble Flt-1 (FIG. 22A) and antibody 27H9 NG/NA AAA (NA+AAA) had similar potency as compared to the non-mutated parent antibody (wt).

Example 6. Antibody Optimization

Candidate antibodies were analyzed to identify the closest human VH and VL germline sequences and to identify differing residues within the framework regions and oxidation/isomerization sites within the CDRs. A Fab library containing human and wild-type residues was constructed and fused to human constant domains. Phage display was applied to identify Fabs with identical or better off rate (i.e., no loss of affinity) than the parent antibody, 21B3. Fabs with the desired off-rate were sequenced and compared to human germline sequence and those with the highest identity (e.g., VH+VL identity >95%) and homology (e.g., >96% homology) were selected for conversion into human monoclonal antibodies. The Fabs are also analyzed for unwanted amino acids. Table 10 provides Fabs ranked by percent human identity with some clones having up to 97.6% human identity and 98.8% homology.

TABLE 10 SORTED BY IDENTITY FAB IDENTITY kd % Ident % Homol IMPROVEMENT Kd 27H4_VH 97.6% 98.8% 1.06 5.1E−04 27H9_VH 97.5% 98.2% 1.12 4.8E−04 25F11_VH 97.5% 98.2% 1.00 5.3E−04 27H6_VH 97.5% 97.5% 0.96 5.6E−04 25A2_VH 97.0% 98.8% 0.97 5.5E−04 27D3_VH 97.0% 98.2% 0.89 6.0E−04 27B4_VH 97.0% 98.2% 0.84 6.4E−04 25D4_VH 97.0% 98.8% 0.94 5.7E−04 25D6_VH 97.0% 98.2% 1.17 4.6E−04 25G9_VH 97.0% 98.2% 0.97 5.5E−04 27C5_VH 97.0% 98.2% 0.96 5.5E−04 25D11_VH 97.0% 98.2% 0.90 6.0E−04 25C8_VH 97.0% 97.5% 0.84 6.3E−04 25G2_VH 96.9% 98.2% 0.81 6.6E−04 27A1_VH 96.4% 98.2% 0.97 5.5E−04 25H3_VH 96.4% 97.5% 0.94 5.7E−04 27F5_VH 96.3% 98.2% 1.18 4.5E−04 25B9_VH 96.3% 98.2% 1.03 5.2E−04 27H1_VH 96.3% 98.2% 0.91 5.9E−04 27G9_VH 96.3% 97.5% 1.30 4.1E−04 27D9_VH 96.3% 97.5% 0.94 5.7E−04 25G8_VH 96.3% 97.5% 0.82 6.5E−04 21B3 96.3% 96.3% 5.3E−04

Example 7. Characterization of Anti-Flt-1 Monoclonal Antibodies

The thermo-tolerance of the monoclonal antibodies was analyzed using a Biacore method. At a concentration of 100 μg/mL, each monoclonal antibody was incubated for 1 hour in phosphate buffered saline at different temperatures. Following the 1 hour incubation, the antibody was slowly cooled to 25° C. over two hours then incubated overnight at 4° C. The percentage of functional antibody was then measured by determining the binding to human Flt-1 by Biocore (see Table 11). The thermo-tolerance for the wild-type antibodies was consistent with previous experiments. However, with the exception of the 27H6 DG/DA clone, mutations in the VH or VL regions reduced the melting temperature by approximately 2° C. The AAA mutation in the Fc region had no effect on the thermo-tolerance of the antibody.

TABLE 11 Tm (° C.) MAB Exp 140421 Exp 140507 Exp 140514 Exp 140613 Exp 140723 Exp 140902 21B3 WT 70.1 70.4 70.9 69.1 70.5 21B3 AAA ~70.8 27H4 WT 67 67.8 ~66.6 67.5 27H4 NG/NA (VH) ~64.1 27H4 NG/QG (VH) ~64.1 27H4 NA + AAA 64.9 27H6 WT 61.9 27H6 DG/DA (VL) ~63.4 27H6 DG/EG (VL) 58.8 27H9 WT 73.8 68.6 69.0 27H9 NG/NA (VH) 66.8 27H9 NG/QG (VH) 66.7 27H9 NA + AAA 67.3

The binding affinity of the humanized clones were analyzed by Biacore (Table 12). The ability to rescue VEGF signaling in a VEGF:sFlt-1 cell based assay was determined for antibodies 27H4, 27H6 and 27H9 (FIG. 22B). Briefly, human primary vein endothelial cells (HUVECs) were stimulated with VEGF in the presence of sFlt-1 and monoclonal antibodies 27H4, 27H6 and 27H9. VEGF induced activation of cells was assayed by determining the phosphorylation status of the VEGF R2 receptor. The data are expressed as a percent rescue of the phosphorylation of the VEGF R2 receptor relative to the phosphorylation of the VEGF R2 receptor in the presence of sFlt-1 alone (e.g., without anti-Flt-1 antibodies). The ability to antagonize binding of VEGF and sFlt-1 (FIG. 23) was also determined for antibodies 27H4, 27H6 and 27H9 by ELISA.

TABLE 12 ka (1/Ms) kd (1/s) Rmax (RU) KD (M) 21B3 5.4E+05 1.7E−04 292 3.2E−10 27H4 3.4E+05 8.2E−05 305 2.5E−10 27H9 3.3E+05 8.4E−05 323 2.6E−10 27H6 9.1E+05 1.4E−04 436 1.6E−10

Example 8. In Vitro Study of Anti-Flt-1 Antibodies on Muscle Pathology

Mdx mice were treated with 1, 3 or 10 mg/kg of anti-Flt-1 antibody 21B3 or 10 mg/kg of IgG1 isotype control antibody by intravenous administration twice a week for 6 or 12 weeks beginning at 3 weeks of age.

To assess serum levels of free antibody concentration, blood was collected from the mice 4 days after the intravenous dose administered at 2, 4, 7 and 10 weeks. The sacrifice sample was collected 24 hours after the last dose (FIG. 24). At the 10 mg/kg dose, there was a statistically significant difference in serum levels of free antibody at all time points relative to the serum levels of free antibody in mice receiving the isotype control antibody. At the 3 mg/kg dose, there was a statistically significant difference in serum levels of free antibody at weeks 4, 7 and 10 and at sacrifice relative to the serum levels of free antibody in mice receiving the isotype control antibody. At the 1 mg/kg dose, there was a statistically significant difference in serum levels of free antibody at sacrifice relative to the serum levels of free antibody in mice receiving the isotype control antibody.

To assess serum levels of free sFlt-1, blood was collected from the mice 4 days after the intravenous dose administered at 2, 4, 7 and 10 weeks. The sacrifice sample was collected 24 hours after the last dose (FIG. 25). At the 10 mg/kg dose, there was a statistically significant difference in serum levels of free sFlt-1 at all time points relative to the serum levels of free sFlt-1 in mice receiving the isotype control antibody. At the 3 mg/kg dose, there was a statistically significant difference in serum levels of free sFlt-1 at weeks 4, 7 and 10 and at sacrifice relative to the serum levels of free sFlt-1 in mice receiving the isotype control antibody. At the 1 mg/kg dose, there was a statistically significant difference in serum levels of free sFlt-1 at sacrifice relative to the serum levels of free sFlt-1 in mice receiving the isotype control antibody.

To assess serum levels of VEGF, blood was collected from the mice 4 days after the intravenous dose administered at 2, 4, 7 and 10 weeks. The sacrifice sample was collected 24 hours after the last dose (FIG. 26). Administration of antibody 21B3 induced a dose dependent increase in serum VEGF levels. At the 10 mg/kg dose, there was a statistically significant difference in serum levels of VEGF at all time points relative to the serum levels of VEGF in mice receiving the isotype control antibody. At the 3 mg/kg dose, there was a statistically significant difference in serum levels of VEGF at week 7 and at sacrifice relative to the serum levels of VEGF in mice receiving the isotype control antibody. At the 1 mg/kg dose, there was a statistically significant difference in serum levels of VEGF at sacrifice relative to the serum levels of VEGF in mice receiving the isotype control antibody.

Histopathology

Mice were sacrificed at weeks 6 and 12 of the treatment period and the diaphragm, gastrocnemius and tibialis anterior muscles were collected and sectioned to determine if treatment with the anti-Flt-1 antibody induced angiogenesis and prevented fibrosis and necrosis in skeletal muscle.

Angiogenesis

Sections of muscle were stained for the endothelial cell marker CD31 (FIGS. 27A-2711, 28A-28H and 29A-29H). A significant increase in capillary density was seen in all muscle groups studied in the mice treated with antibody 21B3 as compared to the muscles of mice treated with the isotype control antibody. The data were quantified using automated quantitative imaging software. There was a statistically significant increase in the CD31 positive area in the diaphragm muscle of mice treated with 3 mg/kg (p<0.01) and 10 mg/kg (p<0.0001) of antibody 21B3 at 6 and 12 weeks as compared to the CD31 positive area in the diaphragm muscle of mice treated with the isotype control antibody. There was a statistically significant increase in the CD31 positive area in the gastrocnemius muscle of mice treated with 10 mg/kg (p<0.05) of antibody 21B3 at 6 and 12 weeks as compared to the CD31 positive area in the gastrocnemius muscle of mice treated with isotype control antibody. There was a statistically significant increase in the CD31 positive area in the tibialis anterior muscle of mice treated with 3 mg/kg of antibody 21B3 at 6 weeks (p<0.05) and 12 weeks (p<0.0001) and of mice treated with 10 mg/kg (p<0.0001) of antibody 21B3 at 6 and 12 weeks as compared to the CD31 positive area in the tibialis anterior muscle of mice treated with the isotype control antibody. (FIGS. 30A-30C).

Fibrosis

Sections of muscle were also stained by immunohistochemistry for type I collagen (FIGS. 31A-31H, 32A-32H and 33A-33H). A significant decrease in type I collagen staining was seen in the diaphragm and gastrocnemius muscle of mice treated with antibody 21B3 as compared to the diaphragm and gastrocnemius muscle of mice treated with the isotype control antibody. There was a statistically significant decrease in the type I collagen staining in the diaphragm muscle of mice treated with 1 mg/kg (p<0.0001), 3 mg/kg (p<0.001) and 10 mg/kg (p<0.0001) of antibody 21B3 at 12 weeks as compared to the type I collagen staining in the diaphragm muscle of mice treated with the isotype control antibody. There was a statistically significant decrease in type I collagen staining in the gastrocnemius muscle of mice treated with 1 mg/kg (p<0.01), 3 mg/kg (p<0.05) and 10 mg/kg (p<0.001) of antibody 21B3 at 12 weeks as compared to the type I collagen staining in the gastrocnemius muscle of mice treated with the isotype control antibody. (FIGS. 34A-34C).

Necrosis

The percentage of necrosis present in the gastrocnemius muscle of mice treated with the 21B3 antibody was determined relative to the percentage of necrosis present in the gastrocnemius muscle of mice treated with the isotype control antibody. A trend toward improvement in necrosis was seen (FIGS. 35A-35B).

Example 9. Mapping of the Epitope on Human sFlt-1 Targeted by Anti-Flt-1 Antibodies 21B3 and 21C6

The peptide level epitopes on human sFlt-1 targeted by anti-human sFlt-1 monoclonal antibodies (mAbs) 21B3 and 21C6 were established by hydrogen deuterium exchange (HDX) mass spectrometry.

Pepsin Digestion and LC-MS

For pepsin digestion, 10 μg of sFlt-1 or sFlt-1 and antibody (21B3) mixture (10 μg:20 μg) or sFlt-1 and antibody (21C6) mixture (10 μg:20 μg) was denatured in 0.365 M TCEP and 1.7 M guanidine hydrochloride (pH 2.5). The mixture was subjected to online pepsin digestion and the resultant peptides were analyzed using an UPLC-MS system comprised of a Waters Acquity UPLC coupled to a MicroTOF-Q2 mass spectrometer (Bruker). The peptides were separated on a 50 mm×1 mm C8 column with a 19 min gradient from 5-28.5% solvent B (0.1% formic acid in acetonitrile). Solvent A is 0.1% formic acid in water. The solvent mixture valve, injection valve, C8 column and all the connecting stainless steel tubings were immersed in a chilled circulating water bath maintained at 0° C. Peptide identification was done through searching MS/MS data against the sFlt-1 sequence with Mascot. The mass tolerance for the precursor and product ions was 0.1 Da and 0.2 Da, respectively.

Deglycosylation Treatment

200 μg of human sFlt-1 recombinant protein was incubated with 10 μl of PNGase F at 37° C. for 4 hrs.

Fab Preparation

Fabs were prepared from two anti-sFlt-1 mAbs (21B3 and 21C6) with papain digestion and Protein A capture using Pierce Fab Preparation Kit.

Size Exclusion Chromatography (SEC)

To check the binding between either native or deglycosylated human sFlt-1 and two anti-human sFlt-1 mAbs (21B3 and 21C6) on SEC, 10 μs of sFlt-1 (either native or deglycosylated) was mixed with 40 μg of anti-sFlt-1 mAbs. Native or deglycosylated sFlt-1 alone, anti-sFlt-1 mAb alone or the complexes were injected to a SEC column at flow rate of 0.35 ml/min with PBS as the mobile phase and the proteins were monitored at 280 nm. Fabs generated from anti-sFlt-1 mAbs (21B3 and 21C6), and the binding between anti-sFlt-1 Fabs and sFlt-1 were also assessed using SEC.

HDX

10 μL human sFlt-1 (10 μg) or sFlt-1 and mAb (21B3) mixture (10 μg:20 μg) or sFlt-1 and mAb (21C6) mixture (10 μg:20 μg) was incubated with 90 μL deuterium oxide labeling buffer (50 mM phosphate, 100 mM sodium chloride at pH 7.4) for 0 s, 30 s, 2 min, 10 min, 1 hr or 4 hr. Deuterium exchange was quenched by adding 100 μL of 3.4 M guanidine hydrochloride, 0.73 M TCEP buffer with a final pH of 2.5, and then subjected to pepsin digestion and LC-MS analysis described above. The mass spectra were recorded in MS only mode. Raw MS data was processed using HDExaminer software (Sierra Analytics, CA). The deuterium levels were calculated using the average mass difference between the deuterated peptide and its native form (t₀).

Results

To verify that glycan removal does not alter the binding of human sFlt-1 to the antibodies, native and deglycosylated sFlt-1 protein were mixed with the anti-human sFlt-1 IgGs (21B3 and 21C6) and the complex formation was monitored on size exclusion chromatography. The data demonstrated that native human sFlt-1 completely binds to the two anti-human sFlt-1 IgGs (21B3 and 21C6) while deglycosylated human sFlt-1 incompletely binds to anti-human sFlt-1 mAb (21B3) or does not bind to anti-human sFlt-1 mAb (21C6), which indicated that deglycosylation perturbs the interactions between human sFlt-1 and the antibodies. Therefore, native human sFlt-1 was selected to perform HD exchange experiments. Poor sequence coverage was achieved initially for native human sFlt-1 due to the high complexity of heterogeneous glycosylation and 12 N-linked glycosylation sites. To improve the sequence coverage, glycan masses at each glycosylation site were identified and high sequence coverage (85.2%) was achieved for native human sFlt-1.

Native human sFlt-1 was incubated in deuterium oxide either alone or in complex with either anti-human sFlt-1 mAb (21B3) or anti-human sFlt-1 mAb (21C6). The deuterium exchange was carried at room temperature for 0 sec, 30 sec, 2 min, 10 min, 60 min and 240 min. The exchange reaction was quenched by low pH and the proteins were digested with pepsin. The deuterium levels at the identified peptides were monitored from the mass shift on LC-MS. The deuterium buildup curves over exchange time for all the peptides were plotted. While most of human sFlt-1 peptides displayed identical or similar deuterium levels with and without anti-human sFlt-1 mAbs (21B3 and 21C6), several peptide segments had significantly decreased deuterium incorporation upon mAb 21B3 or mAb 21C6 binding. Residues 117-129 (corresponding to amino acids 141-153 of SEQ ID NO:90) and 169-182 (corresponding to amino acids 193-206 of SEQ ID NO:90) experienced strong deuterium protection upon binding to anti-human sFlt-1 mAb 21B3, whereas residues 106-114 (corresponding to amino acids 130-138 of SEQ ID NO:90) and 117-124 (corresponding to amino acids 141-148 of SEQ ID NO:90) experienced strong deuterium protection upon binding to anti-human sFlt-1 mAb 21C6. These strongly protected regions were assigned as the epitope peptides for anti-human sFlt-1 mAbs (21B3 and 21C6) and highlighted in blue in the differential heat map shown in FIG. 36 and FIG. 37. The MS/MS spectra for identified peptides containing amino acid residues from epitope regions are shown in FIG. 38A-38E. Peptide 115-124 corresponds to amino acids 139-148 of SEQ ID NO:90; peptide 115-129 corresponds to amino acids 139-153 of SEQ ID NO:90; peptide 154-182 corresponds to amino acids 178-206 of SEQ ID NO:90; peptide 175-180 corresponds to amino acids 119-204 of SEQ ID NO:90; and peptide 104-114 corresponds to amino acids 128-138 of SEQ ID NO:90.

CONCLUSION

85.2% sequence coverage was achieved for human sFlt-1. Residues 117-129 and 169-180 experienced strong deuterium protection upon binding to anti-human sFlt-1 mAb 21B3, whereas residues 106-114 and 117-124 experienced strong deuterium protection upon binding to anti-human sFlt-1 mAb 21C6. These strongly protected regions were assigned as the epitope peptides for the corresponding anti-human sFlt-1 mAb.

EQUIVALENTS AND SCOPE

Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. The scope of the present invention is not intended to be limited to the above Description, but rather is as set forth in the following claims.

TABLE 13 Human Flt-1 amino acid sequence isoform 1 (NP_002010.2 GI: 156104876; SEQ ID NO: 90) 1 MVSYWDTGVL LCALLSCLLL TGSSSGSKLK DPELSLKGTQ HIMQAGQTLH LQCRGEAAHK 61 WSLPEMVSKE SERLSITKSA CGRNGKQFCS TLTLNTAQAN HTGFYSCKYL AVPTSKKKET 121 ESAIYIFISD TGRPFVEMYS EIPEIIHMTE GRELVIPCRV TSPNITVTLK KFPLDTLIPD 181 GKRIIWDSRK GFIISNATYK EIGLLTCEAT VNGHLYKTNY LTHRQTNTII DVQISTPRPV 241 KLLRGHTLVL NCTATTPLNT RVQMTWSYPD EKNKRASVRR RIDQSNSHAN IFYSVLTIDK 301 MQNKDKGLYT CRVRSGPSFK SVNTSVHIYD KAFITVKHRK QQVLETVAGK RSYRLSMKVK 361 AFPSPEVVWL KDGLPATEKS ARYLTRGYSL IIKDVTEEDA GNYTILLSIK QSNVFKNLTA 421 TLIVNVKPQI YEKAVSSFPD PALYPLGSRQ ILTCTAYGIP QPTIKWFWHP CNHNHSEARC 481 DFCSNNEESF ILDADSNMGN RIESITQRMA IIEGKNKMAS TLVVADSRIS GIYICIASNK 541 VGTVGRNISF YITDVPNGFH VNLEKMPTEG EDLKLSCTVN KFLYRDVTWI LLRTVNNRTM 601 HYSISKQKMA ITKEHSITLN LTIMNVSLQD SGTYACRARN VYTGEEILQK KEITIRDQEA 661 PYLLRNLSDH TVAISSSTTL DCHANGVPEP QITWFKNNHK IQQEPGIILG PGSSTLFIER 721 VTEEDEGVYH CKATNQKGSV ESSAYLTVQG TSDKSNLELI TLTCTCVAAT LFWLLLTLFI 781 RKMKRSSSEI KTDYLSIIMD PDEVPLDEQC ERLPYDASKW EFARERLKLG KSLGRGAFGK 841 VVQASAFGIK KSPTCRTVAV KMLKEGATAS EYKALMTELK ILTHIGHHLN VVNLLGACTK 901 QGGPLMVIVE YCKYGNLSNY LKSKRDLFFL NKDAALHMEP KKEKMEPGLE QGKKPRLDSV 961 TSSESFASSG FQEDKSLSDV EEEEDSDGFY KEPITMEDLI SYSFQVARGM EFLSSRKCIH 1021 RDLAARNILL SENNVVKICD FGLARDIYKN PDYVRKGDTR LPLKWMAPES IFDKIYSTKS 1081 DVWSYGVLLW EIFSLGGSPY PGVQMDEDFC SRLREGMRMR APEYSTPEIY QIMLDCWHRD 1141 PKERPRFAEL VEKLGDLLQA NVQQDGKDYI PINAILTGNS GFTYSTPAFS EDFFKESISA 1201 PKFNSGSSDD VRYVNAFKFM SLERIKTFEE LLPNATSMFD DYQGDSSTLL ASPMLKRFTW 1261 TDSKPKASLK IDLRVTSKSK ESGLSDVSRP SFCHSSCGHV SEGKRRFTYD HAELERKIAC 1321 CSPPPDYNSV VLYSTPPI Human Flt-1 amino acid sequence, isoform X1 (XP_011533316.1 GI: 767977511; SEQ ID NO: 91) 1 MVSYWDTGVL LCALLSCLLL TGSSSGSKLK DPELSLKGTQ HIMQAGQTLH LQCRGEAAHK 61 WSLPEMVSKE SERLSITKSA CGRNGKQFCS TLTLNTAQAN HTGFYSCKYL AVPTSKKKET 121 ESAIYIFISD TGRPFVEMYS EIPEIIHMTE GRELVIPCRV TSPNITVTLK KFPLDTLIPD 181 GKRIIWDSRK GFIISNATYK EIGLLTCEAT VNGHLYKTNY LTHRQTNTII DVQISTPRPV 241 KLLRGHTLVL NCTATTPLNT RVQMTWSYPD EKNKRASVRR RIDQSNSHAN IFYSVLTIDK 301 MQNKDKGLYT CRVRSGPSFK SVNTSVHIYD KAFITVKHRK QQVLETVAGK RSYRLSMKVK 361 AFPSPEVVWL KDGLPATEKS ARYLTRGYSL IIKDVTEEDA GNYTILLSIK QSNVFKNLTA 421 TLIVNVKPQI YEKAVSSFPD PALYPLGSRQ ILTCTAYGIP QPTIKWFWHP CNHNHSEARC 481 DFCSNNEESF ILDADSNMGN RIESITQRMA IIEGKNKMAS TLVVADSRIS GIYICIASNK 541 VGTVGRNISF YITDVPNGFH VNLEKMPTEG EDLKLSCTVN KFLYRDVTWI LLRTVNNRTM 601 HYSISKQKMA ITKEHSITLN LTIMNVSLQD SGTYACRARN VYTGEEILQK KEITIRDQEA 661 PYLLRNLSDH TVAISSSTTL DCHANGVPEP QITWFKNNHK IQQEPDADPH IQKADCTFFF Human Flt-1 amino acid sequence, isoform 2 precursor (NP_001153392.1 GI: 229892220; SEQ ID NO: 92) 1 MVSYWDTGVL LCALLSCLLL TGSSSGSKLK DPELSLKGTQ HIMQAGQTLH LQCRGEAAHK 61 WSLPEMVSKE SERLSITKSA CGRNGKQFCS TLTLNTAQAN HTGFYSCKYL AVPTSKKKET 121 ESAIYIFISD TGRPFVEMYS EIPEIIHMTE GRELVIPCRV TSPNITVTLK KFPLDTLIPD 181 GKRIIWDSRK GFIISNATYK EIGLLTCEAT VNGHLYKTNY LTHRQTNTII DVQISTPRPV 241 KLLRGHTLVL NCTATTPLNT RVQMTWSYPD EKNKRASVRR RIDQSNSHAN IFYSVLTIDK 301 MQNKDKGLYT CRVRSGPSFK SVNTSVHIYD KAFITVKHRK QQVLETVAGK RSYRLSMKVK 361 AFPSPEVVWL KDGLPATEKS ARYLTRGYSL IIKDVTEEDA GNYTILLSIK QSNVFKNLTA 421 TLIVNVKPQI YEKAVSSFPD PALYPLGSRQ ILTCTAYGIP QPTIKWFWHP CNHNHSEARC 481 DFCSNNEESF ILDADSNMGN RIESITQRMA IIEGKNKMAS TLVVADSRIS GIYICIASNK 541 VGTVGRNISF YITDVPNGFH VNLEKMPTEG EDLKLSCTVN KFLYRDVTWI LLRTVNNRTM 601 HYSISKQKMA ITKEHSITLN LTIMNVSLQD SGTYACRARN VYTGEEILQK KEITIRGEHC 661 NKKAVFSRIS KFKSTRNDCT TQSNVKH Human Flt-1 amino acid sequence, isoform 3 precursor (NP_001153502.1 GI: 229892300; SEQ ID NO: 93) 1 MVSYWDTGVL LCALLSCLLL TGSSSGSKLK DPELSLKGTQ HIMQAGQTLH LQCRGEAAHK 61 WSLPEMVSKE SERLSITKSA CGRNGKQFCS TLTLNTAQAN HTGFYSCKYL AVPTSKKKET 121 ESAIYIFISD TGRPFVEMYS EIPEIIHMTE GRELVIPCRV TSPNITVTLK KFPLDTLIPD 181 GKRIIWDSRK GFIISNATYK EIGLLTCEAT VNGHLYKTNY LTHRQTNTII DVQISTPRPV 241 KLLRGHTLVL NCTATTPLNT RVQMTWSYPD EKNKRASVRR RIDQSNSHAN IFYSVLTIDK 301 MQNKDKGLYT CRVRSGPSFK SVNTSVHIYD KAFITVKHRK QQVLETVAGK RSYRLSMKVK 361 AFPSPEVVWL KDGLPATEKS ARYLTRGYSL IIKDVTEEDA GNYTILLSIK QSNVFKNLTA 421 TLIVNVKPQI YEKAVSSFPD PALYPLGSRQ ILTCTAYGIP QPTIKWFWHP CNHNHSEARC 481 DFCSNNEESF ILDADSNMGN RIESITQRMA IIEGKNKMAS TLVVADSRIS GIYICIASNK 541 VGTVGRNISF YITDVPNGFH VNLEKMPTEG EDLKLSCTVN KFLYRDVTWI LLRTVNNRTM 601 HYSISKQKMA ITKEHSITLN LTIMNVSLQD SGTYACRARN VYTGEEILQK KEITIRDQEA 661 PYLLRNLSDH TVAISSSTTL DCHANGVPEP QITWFKNNHK IQQEPELYTS TSPSSSSSSP 721 LSSSSSSSSS SSS Human Flt-1 amino acid sequence, isoform 4 precursor (NP_001153503.1 GI:229892302; SEQ ID NO: 94) 1 MVSYWDTGVL LCALLSCLLL TGSSSGSKLK DPELSLKGTQ HIMQAGQTLH LQCRGEAAHK 61 WSLPEMVSKE SERLSITKSA CGRNGKQFCS TLTLNTAQAN HTGFYSCKYL AVPTSKKKET 121 ESAIYIFISD TGRPFVEMYS EIPEIIHMTE GRELVIPCRV TSPNITVTLK KFPLDTLIPD 181 GKRIIWDSRK GFIISNATYK EIGLLTCEAT VNGHLYKTNY LTHRQTNTII DVQISTPRPV 241 KLLRGHTLVL NCTATTPLNT RVQMTWSYPD EKNKRASVRR RIDQSNSHAN IFYSVLTIDK 301 MQNKDKGLYT CRVRSGPSFK SVNTSVHIYD KAFITVKHRK QQVLETVAGK RSYRLSMKVK 361 AFPSPEVVWL KDGLPATEKS ARYLTRGYSL IIKDVTEEDA GNYTILLSIK QSNVFKNLTA 421 TLIVNVKPQI YEKAVSSFPD PALYPLGSRQ ILTCTAYGIP QPTIKWFWHP CNHNHSEARC 481 DFCSNNEESF ILDADSNMGN RIESITQRMA IIEGKNKLPP ANSSFMLPPT SFSSNYFHFL 541 P

TABLE 14 Fc Region Sequence (SEQ ID NO: 104) 209 TKVDKKVEPK SCDKTHTCPP CPAPELLGGP SVFLFPPKPK DTLMISRTPE VTCVVVDVSH 269 EDPEVKFNWY VDGVEVHNAK TKPREEQYNS TYRVVSVLTV LHQDWLNGKE YKCKVSNKAL 329 PAPIEKTISK AKGQPREPQV YTLPPSREEM TKNQVSLTCL VKGFYPSDIA VEWESNGQPE 389 NNYKTTPPVL DSDGSFFLYS KLTVDKSRWQ QGNVFSCSVM HEALHNHYTQ KSLSLSPG 

1. An antibody or antigen-binding fragment thereof that specifically binds to human Flt-I comprising one or more complementarity determining regions (CDR) selected from the group consisting of (a) a variable light (VL) chain CDR1 defined by an amino acid sequence having at least 90% identity to SEQ NO:21; a VL CDR2 defined by an amino acid sequence having at least 90% identity to SEQ ID NO:24; a VL CDR3 defined by an amino acid sequence having at east 90% identity to SEQ ID NO:26; a variable heavy (VH) chain CDR1 defined by an amino acid sequence having at least 90% identity to SEQ ID NO:2; a VH CDR2 defined by an amino acid sequence having at least 90% identity to any one of SEQ ID NO:6, and a VH CDR3 defined by an amino acid sequence having at least 90% identity to any one of SEQ ID NO:16. (b) a VL CDR1 defined by the amino acid sequence having at least 90% identity to SEQ ID NO:21, a VL CDR2 defined by the amino acid sequence having at least 90% identity to SEQ ID NO:24, a VL CDR3 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 27, a VH CDR1 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 2, a VH CDR2 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 7, and a VH CDR3 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 17; (c) a VL CDR1 defined by the amino acid sequence having at least 90% identity to SEQ ID NO:21, a VL CDR2 defined by the amino acid sequence having at least 90% identity to SEQ ID NO:24, a VL CDR3 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 26, a VH CDR1 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 3, a VH CDR2 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 12, and a VH CDR3 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 17; (d) a VL CDR1 defined by the amino acid sequence having at least 90% identity to SEQ ID NO:21, a VL CDR2 defined by the amino acid sequence having at least 90% identity to SEQ ID NO:24, a VL CDR3 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 28, a VH CDR1 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 2, a VH CDR2 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 8, and a VH CDR3 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 17; or (e) a VL CDR1 defined by the amino acid sequence having at least 90% identity to SEQ ID NO:21, a VL CDR2 defined by the amino acid sequence having at least 90% identity to SEQ ID NO:24, a VL CDR3 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 32, a VH CDR1 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 3, a VH CDR2 defined by the amino acid sequence having at least 90% identity to SEQ ID NO: 12, and a VH CDR3 defined by the amino acid sequence having at least 90% identity to SEQ ID NO:
 17. 2.-15. (canceled)
 16. An antibody or antigen-binding fragment thereof of claim 1 that specifically binds to human Flt-1, comprising: (i) a light chain variable (VL) region comprising an amino acid sequence having at least 80% identity to any one of SEQ ID NO:49 to SEQ ID NO:61, and/or (ii) a heavy chain variable (VH) region comprising an amino acid sequence having at least 80% identity to any one of SEQ ID NO:35 to SEQ ID NO:48.
 17. The antibody or antigen-binding fragment thereof of claim 16, wherein the VL region comprises the amino acid sequence of SEQ ID NO: 60 and the VH region comprises the amino acid sequence of SEQ ID NO:45.
 18. The antibody of claim 1, wherein the antibody further comprises a heavy chain constant region comprising an amino acid sequence having at least 80% identity to any one of SEQ ID NO:87 to SEQ ID NO:89.
 19. An antibody or antigen-binding fragment thereof that specifically binds to human Flt-I, comprising: (i) a light chain comprising an amino acid sequence having at least 80% identity to any one of SEQ II) N0:75 tot SEQ ID NO:86, and/or (ii) a heavy chain comprising an amino acid sequence having at least 80% identity to any one of SEQ ID NO:62 to SEQ ID NO:74.
 20. The antibody or antigen-binding fragment thereof of claim 19, wherein the light chain comprises the amino acid sequence of SEQ ID NO:76 and the heavy chain comprises the amino acid sequence of SEQ ID NO:71.
 21. The antibody or antigen-binding fragment thereof of claim 1, wherein the antibody or antigen-binding fragment thereof is selected from the group consisting of IgG, F(ab′)2, F(ab)2, Fab′, Fab, ScFvs, diabodies, triabodies and tetrabodies.
 22. The antibody or antigen-binding fragment thereof of claim 21, wherein the antibody or antigen-binding fragment thereof is IgG.
 23. (canceled)
 24. The antibody or antigen-binding fragment thereof of claim 1, wherein the antibody or antigen-binding fragment thereof is a monoclonal antibody.
 25. (canceled)
 26. The antibody or antigen-binding fragment thereof of claim 24, wherein the monoclonal antibody contains a human Fc region.
 27. The antibody or antigen-binding fragment thereof of claim 26, wherein the Fc region contains one or more mutations that enhance the binding affinity between the Fc region and the FcRn receptor such that the in vivo half-life of the antibody is prolonged.
 28. (canceled)
 29. The antibody or antigen-binding fragment thereof of claim 1, wherein the antibody or antigen-binding fragment thereof does not bind to VEGFR2 and/or VEGFR3.
 30. The antibody or antigen-binding fragment thereof of claim 1, wherein the antibody or antigen-binding fragment thereof does not bind to a mouse or monkey Flt-1. 31.-32. (canceled)
 33. An isolated antibody or antigen-binding fragment thereof that competes with the antibody or antigen-binding fragment thereof of claim
 1. 34. A pharmaceutical composition comprising the antibody or antigen-binding fragment thereof of claim 1 and a pharmaceutically acceptable carrier. 35.-39. (canceled)
 40. A method for treating a Flt-1-mediated disease, disorder or condition comprising administering to a subject in need of treatment the antibody or antigen-binding fragment thereof of claim
 1. 41. The method of claim 40, wherein the Flt-1-mediated disease, disorder or condition is Duchenne muscular dystrophy, Becker muscular dystrophy, preeclampsia or chronic kidney disease.
 42. A method of treating Duchenne Muscular Dystrophy (DMD), the method comprising: administering to a subject who is suffering from or susceptible to DMD an effective amount of the antibody or antigen-binding fragment thereof of claim 1, such that at least one symptom or feature of DMD is reduced in intensity, severity, or frequency, or has delayed onset. 43-44. (canceled)
 45. The method of claim 42, wherein the antibody or antigen-binding fragment thereof is administered parenterally.
 46. The method of claim 45, wherein the parenteral administration is selected from intravenous, intradermal, intrathecal, inhalation, transdermal (topical), intraocular, intramuscular, subcutaneous, and/or transmucosal administration. 47.-60. (canceled) 